We determined the acute and chronic toxicity of aniline to tilapia (Oreochromis mossambicus), cladoceran crusatcea (Moina micrura) and oligochaete worm (Branchiura sowerbyi) using static bioassay tests. The 96h LC50 values of aniline for O. mossambicus, M. micrura and B. sowerbyi were 69.4, 0.6 and 586 mg l(-1) respectively. Tilapia responded to even low concentrations of aniline: the fish lost appetite at aniline concentrations as low as 0.02 mg l(-1). A 90 d outdoor bioassay with tilapia showed that 0.02 mg l(-1) aniline reduced fish yield, specific growth rate and food conversion efficiency. Reproductive functions of fish were affected by aniline at a concentration of 0.5 mg l(-1) and above. Dissolved oxygen, primary productivity and plankton population of the test medium also were significantly reduced at 2.65 and 6.94 mg l(-1) aniline.