Orechromis niloticus fingerlings were exposed to the insect growth inhibitor diflubenzuron 1-(2,6-Difluorobenzoyl)3-(4-chlorophenyl)urea for 21 days. Diflubenzuron was introduced to the aquariums where fish were maintained at the beginning of the experiment, then its level in water, gills and liver was detected after 1, 7, 14 and 21 days. The fish accumulated diflubenzuron 76 and 99 times greater than the water content when kept in an ambient concentration of 2.5 and 5 mg/l, respectively, indicating a low bioaccumulation potential. Some degradation products of diflubenzuron were found mainly in liver and water.