Sodium colistimethate (Coly-Mycin Injectable) was administered intravenously to eight patients with Pseudomonas infections in doses of 2 to 2.5 mg/kg every 12 hours. Bacteriologic cure was achieved in five patients. The resulting serum concentrations of sodium colistimethate were approximately twice those obtained following intramuscular administration. Probenecid (Benemid) did not augment serum levels of the antibiotic. In the presence of moderately impaired renal function the intravenous dose should be decreased to 1 mg/kg every 12 hours. In severe renal failure, a dose of 2 mg/kg every two to three days should not be exceeded.