Twenty-two patients with advanced colorectal cancer (CRC) (12 without prior chemotherapy) and fourteen with pretreated breast cancer (BC) were given mitozolomide (MTZ), IV infusion, every six weeks. The starting dose was 90 mg/m2. When it was well-tolerated, dose escalation was done up to 100-115 mg/m2. Toxicity was mild, limited to thrombocytopenia with a median nadir of 1.27 x 10(5) (0.20-4.86). No response was observed in these patients. MTZ, according to these schedule and dosage, does not show activity in human CRC and pretreated BC.