In a phase II study of methyl-glyoxal bis-guanylhydrazone (methyl-GAG) in patients with bi-dimensionally measurable metastases of renal cell cancer, 30 patients were given 500 mg/m2 weekly for at least 4 treatment cycles and were evaluable for response. Three patients (10%) achieved partial remission (PR) with a duration of 8-12 weeks; in 11 patients the disease was assessed as stable; and in 16 there was progression. A total of 40 patients were evaluable for toxicity. Nausea and vomiting occurred in 17 (43%), neuropathy, myopathy or myalgia in 8 (21%) and mucositis in 6 (14%). In addition to 3 patients taken off treatment before 4 treatment cycles, toxicity precluded further treatment in 3 others after 5, 6 and 7 cycles respectively. Methyl-GAG has minimal activity in renal cell cancer and, in this dose schedule, causes appreciable toxicity.