The aim of the study was to determine the effect of volume resuscitation on serum concentrations of cefazolin after severe multiple trauma: prospective and follow-up in a 6-bed trauma intensive care unit, university hospital (10 multiple trauma patients, injury severity score [ISS] > 17 patients).Measurements of serum concentrations were done before, 0.5 and 4 hours after intravenous administration of 2 g cefazolin. The standard regimen of cefazolin administration was 2 g every eighth hour for 48 hours. The data are presented as median, minimum, maximum. Ten patients with an ISS of 29 (18 to 41) points and an age of 32 (22 to 77) years were included. The patients received a total of 9,700 (3,500 to 24,500) ml kristalloid solutions and median 3,800 (500 to 10,400) ml of blood and fresh frozen plasma on the day of the measurements. Before implementation of the measurements, all patients received a total dose of cefazolin between 4 and 10 g. Serum concentrations were 7 (6 to 27) mg/l immediately before start of the infusion (8 hours after the last administration), 186 (36 to 641) mg/l after 0.5 hours and 19 (11 to 60) mg/l at 4 hours after cessation of infusion. The serum concentrations did not correlate with the total doses of cefazolin given before implementation of the measurements.The measured median serum concentrations of cefazolin after an interval of application of 8 hours were much lower than the needed minimum inhibitory serum concentrations against Staphylococcus (10 mg/l). To avoid low minimum serum concentrations and increase the efficacy of prophylactic antibiotic administration a shorter interval of application should probably be chosen.