SummaryThe present study was carried out in order to evaluate the mutagenic effect of 3 nitrogenous fertilizers; urea, ammonium nitrate and calcium nitrate; on Drosophila melanogaster. Newly hatched larvae were treated with the LC 25 and LC 50 of the 3 tested nitrogenous fertilizers. The classic sex-linked recessive lethal (SLRL) test was used to detect the differential mutagenic effect of the fertilizers on the 3 germ stages. The results showed that all fertilizers exhibited variable mutation frequencies in the different broods of spermatogenesis after a single treatment. Urea exhibited a direct mutagenic effect on post-meiotic stages whereas ammonium nitrate and calcium nitrate revealed an indirect mutagenic effect on meiotic and pre-meiotic stages. The electrophoretic separation of proteins (SDS-PAGE) showed that treatment with these fertilizers resulted in polymorphetic changes in different low and high molecular weight protein bands, causing alteration in the electrophoretic patterns and densities of proteins. This study showed that the tested nitrogenous fertilizers possess mutagenic potentialities which are related to their nitrogen content.