The most commonly used test for evaluating the toxicity of effluents to fish and invertebrates has been the acute lethality test. However, effluents frequently are not acutely toxic, and so assessing the sublethal effects on fish and invertebrates is important. Described herein is a rapid method to estimate the chronic toxicity of effluents to the fathead minnow (Pimephales promelas). Tests are initiated using newly hatched minnow larvae and are run for 7 d under static-renewal conditions. It is a cost-effective, simple, short-term toxicity test, and survival and growth are the measures of effects. Approximately 70 tests using this technique have been run with various types of effluents. Included in this article are results from representative effluent tests and also from tests conducted using Dursban, zinc and copper. The results indicate that this subchronic toxicity test gives a good estimate of chronic toxicity.