The clinical effect of measuring serum gentamicin concentrations and individualizing each patient's dosage regimen was determined 105 burn patients with severe gram-negative sepsis. Thirty-nine patients (conventionally dosed group) received the recommended dosage regimen of 3 to 5 mg/kg/day from 1972 to 1974. From 1974 to 1976, serum concentrations were measured in 66 patients (individually dosed group), and each patient's dose was individually calculated to obtain therapeutic serum concentrations. All patients had normal renal function prior to initiation of gentamicin therapy. For each group, 16 independent variables were compared that may have influenced treatment response. The patients in the individually dosed group required an average dose of 7.4 mg/kg/day to achieve therapeutic concentrations, compared to the average dose of 4.4 mg/kg/day for the patients receiving conventional doses (P less than 0.001). An abrupt increase in patient survival occurred with the implementation of individualized regimens. Patient survival rates for the entire hospital course were 33% and 64% for the conventionally dosed and individually dosed groups, respectively (P less than 0.005). Survival rates for the first septic episode were 51.3% and 86.4%, respectively (P less than 0.001). Individualized gentamicin regimens, age, percent burn, and sex were the statistically significant variables related to patient survival for the first episode of sepsis. Age, percent burn, individualized dosing, complications during hospitalization, and a positive blood culture were significant factors related to patient survival for the entire hospital course. These data confirm the need for measuring serum gentamicin concentrations and adjusting dosages to ensure therapeutic levels and maximal efficacy of gentamicin in burn patients.