Human spermatozoa were exposed to Mitomycin C (MM() at the concentrations of 7.5, 15, 3O micrograms/ml for 1 hour respectively before interspecific in vitro fertilization with zona-free hamster ova. The first cleavage metaphases was analyzed to investigate MMC-induced effects on human spermatozoa. The results showed a distinct dose-response relationship in the induction of chromosomal aberrations. The chromatid aberrations were the predominant types in MMC-induced changes. Some chromosome-type aberrations were also observed. This suggested that the induced effects of MMC on human spermatozoa were some different from that of ultraviolet light-like clastogens on somatic cells. 36.89% of MMC-induced aberrations were rejoining-type. This indicated that the DNA repair systems present in golden hamster oocytes were effective in repairing MMC-induced DNA lesions in human spermatozoa.