Considering environmental pollution problems and their impact on man, we have developed a research programme on environment monitoring. The aim of this work was to develop and to apply radiochemical methods for the analysis of cesium-137 in marine samples, such as seawater and fish. Cesium-137 levels in surface seawater from the coastal region of Sao Paulo State range from 1.7 to 1.9 Bq . m-3. Samples of the five species of fish most consumed by local population were taken for the analysis of cesium-137. Levels for fish varied from 0.1 to 0.3 Bq . kg-1 of edible part. Data were used to calculate dose assessment.