Further to a Manual on Sampling and Analyses of Biological Material (FAO Fish. Tech. Pap. 158), this Manual on Statistical Tests has been prepared to assist laboratories participating in the FAD/UNEP project in proper planning of monitoring programmes and research projects, and to facilitate the evaluation of data and results obtained. However, although the examples in the manual were chosen to specifically suit the FAD/UNEP project, this manual is expected to be of use to all laboratories involved in analysing pollution levels and measuring effects of pollution on aquatic life.