Gentamicin is commonly administered by intermittent infusions using a gravity-flow or a mechanical device. The primary objective of our study was to compare the pharmacokinetic data in patients receiving gentamicin infusion by a syringe pump and a new controlled-release membrane infusion device. The membrane device consists of a drug and a fluid chamber separated by a 0.2-micron proprietary membrane; drug transfer is based on electrodiffusion across the membrane. Ten patients (mean age 50 years) received the same dose of gentamicin, separated by a 24-h interval, from two devices. Differences in serum concentrations, distribution volume, and half-life were not statistically significant. However, time for complete delivery (0.9 +/- 0.4 h for membrane device vs. 0.5 h for syringe pump) and calculated dosage requirements (10.9 +/- 6.3 vs. 9.6 +/- 5.5 mg/h) to achieve peak of 7 and trough of 1 microgram/ml were significantly different (p less than 0.05). Thus, the infusion method for gentamicin can have a significant influence on its pharmacokinetic monitoring.