Pharmacologic studies of the semisynthetic cephalosporin ceforanide were conducted in 29 cancer patients. Intravenous doses of 500 mg over 30 min every 6 hr to 10 patients induced mean peak serum concentrations between 44.7 and 51.5 micrograms/ml, while in 10 patients receiving 1 gm over 30 min every 12 hr mean peak serum concentrations varied from 73.4 to 91.8 micrograms/ml. Twelve hours after 1 gm of drug, mean serum concentrations varied between 5.6 and 6.5 micrograms/ml. After a 500-mg loading dose, continuous infusion of 500 mg every 4 hr, 10 patients maintained serum concentrations above 34.2 micrograms/ml for 7 or 8 days. Most of the drug was excreted in the urine in the initial 6 hr after administration and mean urinary concentration of 1,315 micrograms/ml were obtained during this time. Serum half-life ranged between 2.2 and 2.9 hr on all schedules and therefore wa longer than that of other cephalosporins. No serious toxicity was noted. The relatively broad spectrum of activity in addition to the long half-life suggests clinical utility for this drug.