Pharmacokinetics of temocillin (BRL 17421) was studied in a crossover study in 10 male healthy volunteers after administration 1 g of temocillin intravenously or intramuscularly. The mean serum levels of temocillin at the 5th min after i.v. administration were 131.57 mg/ml, at 1 h 71.27 mg/l and at 12.12 mg/l. The values of the pharmacokinetic parameters were as follows: AUC 509.2 mg X h X l-1, t1/2 4.2 h-1, Vd ss 11.57 l, Vd area 12.28 l, CL 2049 ml X h-1. The urinary excretion by 12 h was 70.58% of the administered dose of temocillin. The mean serum levels of temocillin after i. m. administration were at 2 h 46.65 mg/l and at 12 h 15.89 mg/l, the corresponding pharmacokinetic parameters were: AUC 501.38 mg X h X l-1, t1/2 4.3 h-1, Vd 12.69 l. The urinary excretion by 12 h was 57% of the administered dose of temocillin. It follows from the study that pharmacokinetic parameters of temocillin after both ways of temocillin administration are very closed and that the dose 1 g of temocillin is sufficient to create effective serum levels for the majority of sensitive gramnegative organismus.