A series of static short-term bioassays was conducted to assess the acute toxicity of the plant Euphorbia kamerunica on the fingerlings of Oreochromis niloticus. The 96-h LC(50) was computed using two methods: probit analysis and the arithmetic graphic method. The overall mean value of 0.023 +/- 0.002 g/L was obtained. Aquatic invertebrates are generally much more sensitive than fish species. Poisoning of streams with this plant to capture fish may therefore have ecological consequences, as nontarget aquatic animals may be killed in the process. Water quality standards for the protection of aquatic life are based on toxicity data for the most sensitive species found in the aquatic environment. We therefore suggest that E. kamerunica should not be used directly in freshwater bodies without detailed studies of its long-term effects on nontarget organisms as well its structure-activity relationship.