Two hundred and eighty-one patients received 927 doses of cis-platinum, generally on an outpatient basis, at 55 mg/m2 every 3-4 weeks. Mannitol and 2.2501 of hydration with saline and 5% dextrose plus NaCl and KCl were given in 3-4 hr. No case of acute renal failure ensued and when azotemia occurred (3.5% of patients) it was easily reversible and controlled. An abnormal level of one or more electrolytes was detected in 194 patients (69%) during chemotherapy. K+, Na+, Ca2+ and Mg2+ values usually decreased in serum after DDP administration, but their depletion seldom caused symptoms. Hypomagnesemia developed in 20% of patients, but was symptomatic in only 1%. cis-Platinum, at the doses utilized, is safely given to outpatients, with the hydration program employed. Serum electrolyte decrease during chemotherapy must be expected, and rapidly corrected when symptoms develop.