Using a biochemical indicator, the effects of fecal pollution in the estuary of the Nakdong river and in the Chinhae Hay were investigated from summer to winter in 1997-1998. The biochemical indicator used in this study was coprostanol (5-cholestan-3-ol) which is a kind of fecal sterol. It is a useful tracer of fecal pollution, as it is only found in feces of mammals including humans. Coprostanol was less affected by surrounding environments than other indicators of fecal pollution such as fecal coliform or ammonium and was proved to be a good indicator of fecal pollution. Therefore, long-term observations of coprostanol and related compounds could be used as useful indicators for the effects of feces on marine environments and ecosystems.