A Chinese hamster cell mutant (V-C8) isolated previously, which is approximately 100 fold more sensitive to mitomycin C (MMC) than its parental wild-type V79 cells (judged by D10 values), was further characterized. V-C8 cells exhibit an increased sensitivity towards other cross-linking agents, such as cis-DDP (approximately 40-fold), DEB (approximately 30-fold), and also to adriamycin (approximately 5-fold), and the monofunctional alkylating agents: MMS (approximately 5-fold) and EMS (approximately 6-fold). V-C8 cells show a higher level induction of chromosomal aberrations by cross-linking agents (MMC, cis-DDP, and DEB) and an increased level of spontaneous chromosomal aberrations in comparison to the wild-type V79 cells. To determine whether the V-C8 mutant represents a new complementation group among Chinese hamster cell mutants that also display the extreme sensitivity to MMC, V-C8 cells were fused with irs1, irs1SF, UV20, UV41, and V-H4 cells. In all cases, the derived hybrids regained the MMC sensitivity similar to wild-type cells, indicating that the V-C8 mutant belongs to a new sixth complementation group.