To evaluate the use of native fish species for assessing genotoxic pollution in the marine environment, micronucleus (MN) analysis was performed in peripheral blood erythrocytes and gill cells of the grey mullet (Mugil cephalus) from three sampling stations off the southeastern Mediterranean coast of Turkey. The frequencies of blebbed, notched, and lobed nuclei and binucleated cells also were evaluated in peripheral erythrocytes. The sampling sites were chosen on the basis of pollution levels; Karaduvar harbor, contaminated by different types of industrial effluents, and Mersin harbor, mainly contaminated by aromatic hydrocarbons, were selected as polluted areas. Erdemli harbor, a relatively unpolluted site, was used as the control area. Sampling was carried out at four different seasons. The frequencies of both micronuclei and other nuclear abnormalities (NAs) in mullets captured from polluted areas were significantly higher than those in mullets from the reference area. In general, gill cells had considerably higher MN frequencies than did erythrocytes, and genotoxic responses were higher in summer than in winter. The results of this study indicate that the MN test in fish is a suitable biomarker for in situ monitoring of genotoxic pollution in the marine environment. As demonstrated in this study, NAs other than micronuclei are also useful indices of chemical exposure and toxic responses. Therefore, measuring both micronuclei and NAs may increase the sensitivity of the test system.