Pharmacokinetic parameters of ceftriaxone were studied on day 1 and 5 in 21 patients admitted in an ICU for severe infections. All patients received a single daily infusion of 2 g of ceftriaxone during 15 minutes. We have determined the ratio to the daily dose of serum ceftriaxone concentrations (peak level and trough level) and of areas under the curve. According to renal function and the existence of cholestasis, the results of our study showed: 1) In patients with creatinine clearance greater than 10 ml/mn and without cholestasis, a single daily infusion of 2 g ceftriaxone achieves therapeutic blood levels without any accumulation phenomenon. 2) In patients requiring hemodialysis without cholestasis, the period between two 2 g doses should be prolonged to 48 h. 3) Marked cholestasis and creatinine clearance greater than 10 ml/mn prolong the elimination half-life of ceftriaxone leading to an interval extension of the single dose of 2 g. Further investigations are needed in the latter situation.