Fifteen patients less than 2 months old with bacterial infections caused by pathogens known or presumed to be sensitive to cefoxitin were studied. Cefoxitin was administered as an i.v. bolus injection over 15 min, every 8 h for 6 to 12 days, to a total daily dosage of 90 mg/kg. In 14 patients cefoxitin therapy resulted in eradication of the pathogen and in recovery from clinical signs of infection. Only one patient did not respond to cefoxitin therapy. No adverse clinical or haematological effects definitely caused by cefoxitin were observed. Plasma and urine samples collected after the first dose were assayed for cefoxitin by HPLC. Pharmacokinetic data indicated larger apparent volume of distribution (0.5 1/kg), a smaller plasma clearance (0.27 1/h/kg) and a longer half-life (1.43 h) than in adults. The plasma half-life was inversely correlated (p less than 0.05) to the postnatal age of the patients. Cefoxitin may be safely used in infants with infections caused by susceptible pathogens.