The effectiveness of a new mitomycin derivative, KW2149, against human tumors was evaluated by the 4 days subrenal capsule assay (SRCA) and the nude mice screening assay (NMSA). Evaluation by the SRCA showed a 50% response rate at a maximum dose of 3.8 mg/kg for 3 consecutive days. When evaluated by NMSA, the response rate was 100, 75 and 25% after the intermittent administration of 7.5, 5.6 and 4.5 mg/kg (q4dx3) respectively. Although the efficacy was reduced when mice were administered a single dose equivalent to the intermittent one, the new analog was along more effective than MMC administered by either modality.