This report gives a summary of the monitoring activities within the national Swedish contaminant programme in marine biota. It is the result from the joint efforts of: the Department of Applied Environmental Science at Stockholm University (analyses of organochlorines), the Department of Environmental Assessment at Swedish University of Agricultural Sciences (analyses of heavy metals), Department of Chemistry at Umeå University (analyses of PCDD/PCDF) and the Department of Contaminant Research at the Swedish Museum of Natural History (co-ordination, sample collection administration, sample preparation, recording of biological variables, storage of frozen biological tissues in the Environmental Specimen Bank for retrospective studies, data preparation and statistical evaluation). The monitoring programme is financiated by the Environmental Protection Agency (EPA) in Sweden.The data of concern in this report represent the bioavailable part of the investigated contaminants i.e. the part that has virtually passed through the biological membranes and may cause toxic effects. The objectives of the monitoring program in marine biota could be summarised as follows:• to estimate the levels and the normal variation of various contaminants in marine biota from several representative sites, uninfluenced by local sources, along the Swedish coasts. The goal is to describe the general contaminant load and to supply reference values for regional and local monitoring programmes• to monitor long term time trends and to estimate the rate of found changes.quantified objective: to detect an annual change of 10% within a time period of 10 years with a power of 80% at a significance level of 5%.• to estimate the response in marine biota of measures taken to reduce the discharges of various contaminantsquantified objective: to detect a 50% decrease within a time period of 10 years with a power of 80% at a significance level of 5%.• to detect incidents of regional influence or widespread incidents of ‘Chernobyl’- character and to act as watchdog monitoring to detect renewed usage of banned contaminants.quantified objective: to detect an increase of 200% a single year with a power of 80% at a significance level of 5%.• to indicate large scale spatial differencesquantified objective: to detect differences of a factor 2 between sites with a power of 80% at a significance level of 5%.• to explore the development and regional differences of the composition and pattern of e.g. PCB’s, HCH’s and DDT’s as well as the ratios between various contaminants.• the time series are also relevant for human consumption since important commercial fish species like herring and cod are sampled. A co-operation with the Swedish Food Administration is established. Sampling is also co-ordinated with SSI (Swedish Radiation Protection Authority) for analysing radionuclides in fish and blue mussels (HELCOM, 1992).• all analysed, and a large number of additional specimens, of the annually systematically collected material are stored frozen in the Environmental Specimen Bank.. This invaluable4material enables future retrospective studies of contaminants impossible to analyse today as well as control analyses of suspected analytical errors.• although the programme is focused on contaminant concentration in biota, also the development of biological variables like e.g. condition factor (CF), liver somatic index (LSI) and fat content are monitored at all sites. At a few sites, integrated monitoring with fish physiology and population are running in co-operation with the University of Gothenburg and the Swedish Board of Fisheries.• experiences from the national programme with several time series of over 25 years can be used in the design of regional and local monitoring programmes.• the perfectly unique material of high quality and long time series is further used to explore relationships among biological variables and contaminant concentrations in various tissues; the effects of changes in sampling strategy, the estimates of variance components and the influence on the concept of power etc.• the accessibility of high quality data collected and analysed in a consistent manner is an indispensable prerequisite to evaluate the validity of hypothesis and models concerning the fate and distribution of various contaminants. It could furthermore be used as input of ‘real’ data in the ongoing model building activities concerning marine ecosystems in general and in the Baltic and North Sea environment in particular.• the contaminant programme in marine biota constitute an integrated part of the national monitoring activities in the marine environment as well as of the international programmes within ICES, OSPARCOM and HELCOM.The present report displays the timeseries of analysed contaminants in biota and summarises the results from the statistical treatment. It does not in general give the background or explanations to significant changes found in the timeseries. Increasing concentrations thus, urge for intensified studies.Short comments are given for temporal trends as well as for spatial variation and, for some contaminants, differences in geometric mean concentration between various species caught at the same site. Sometimes notes of seasonal variation and differences in concentration between tissues in the same species are given. This information could say something about the relative appropriateness of the sampled matrix and be of help in designing monitoring programmes. In the temporal trend part, an extract of the relevant findings is summarised in the 'conclusion'-paragraph. It should be stressed though, that geographical differences may not reflect antropogenic influence but may be due to factors like productivity, temperature, salinity etc.The report is continuously updated. The date of the latest update is reported at the beginning of each chapter. The creation date of each figure is written in the lower left corner.