We studied the pharmacokinetics and efficacy of cefotaxime in 32 neonates with severe gram-negative infections. Many of these patients had been treated unsuccessfully with combinations of antibiotics. Eighty-one percent of these patients were cured, 6% improved, and 13% had treatment failures; there were three deaths. Eighteen patients received cefotaxime alone; 16 were cured and two improved. These data indicate an efficacy of cefotaxime sufficient to warrant more rigorous future trials. The elimination half-life of cefotaxime ranged from 2.0 +/- 0.4 hours in term neonates more than one week of age to 5.7 +/- 0.8 hours in preterm neonates less than one week of age. A volume of distribution of approximately 0.63 L was similar for all infants irrespective of age and maturity. These kinetic data can be used in design of future therapeutic regimens in more rigidly controlled trials assessing indications for cefotaxime therapy in neonates. We recommend dosing as follows, using a dose of 25 mg/kg: every 12 hours for preterm infants less than one week of age, every 8 hours for preterm infants one to four and term infants less than one week of age, and every 6 hours for term infants more than one week of age.