The present manual makes only cursory reference to the techniques used to study the sublethal toxic effects at the "individual" level of organisation or below since it is devoted to biological studies at community level and especially to the use of benthos. It describes how a benthic sampling programme should be designed so that the data collected can be best interpreted and evaluated. Information is provided for the collection and treatment of the samples as well as for the analysis of the data using statistical methods and computer software. Multivariate analysis techniques include hierarchical clustering, multi-dimensional scaling ordination and principal components analysis.