In Drosophila melanogaster, somatic gene mutagenicity and killing effect of IQ, Trp-P-2, EMS, MMC known as positive mutagens were examined by using (w^i)₄ a new eye-color mutation assaying system. By analysis of these results, whether (w^i)₄ system can be used as sensitive system of environmental mutagens and carcinogens, genotoxic effects of mutagens was investigated. In (w^i)₄ system, the frequency of spontaneous somatic gene mutation was nearly 1.06%. The frequencies of heterocyclic amines, IQ-indued mutations were 1.44% at 0.1㎎/㎖, and 1.62% at 0.3㎎/㎖. In Trp-P-2, the mutation frequencies were 2.20% at 0.5㎎/㎖ and 2.70% at 1.0㎎/㎖. Therefore, (w^i)₄ system was showed positive response to mutagenicity in all the groups treated with IQ and Trp-P-2. The mutation frequencies of groups treated with alkylating agents, EMS, were 4.04% at 5mM and 6.32% at 10mM. Those of groups treated with MMC were obtained 1.76% at 8μM, 1.87% at 16μM, and 1.64% at 24μM. In comparing mutation frequency of each mutagen with that of other assaying system, (w^i)₄ system was occurred higher frequency than uz system and w^i system. Hence, it was confirmed that (w^i)₄ system was the sensitive assaying system, which could detect environmental mutagens and carcinogens by way of evaluating even fewer the number of flies.