Thirty patients (17 male, 13 female; age 17 to 84 years; normal renal function in 23 cases) with severe bacterial infections were treated with ceftriaxone. The infections was septicemia in 20 cases, a septicemia-like condition in 2 and a focal infection in 8 (2 abscesses of the lung, 2 pyelonephritis, 1 abscess of the liver, 1 subphrenic abscess, 1 meningitis developed from an abscess of the brain and 1 acute intestinal infection). 25 infections were bacteriologically documented, with recovery of the following pathogens: 20 Gram negative rods (including 10 E. coli) that were all susceptible to ceftriaxone (MIC = 0.02 to 0.5 mg/l) except 2 (1 Pseudomonas and 1 E. cloacae), 5 susceptible Gram positive cocci (3 Pneumococcus, 1 Streptococcus and 1 Staphylococcus epidermidis) and 3 susceptible anaerobes (2 B. fragilis and 1 B. melaninogenicus). Ceftriaxone was given alone in 15 cases and in association with another antibiotic in 15 cases (aminoglycoside in 10 cases, nitroimidazole in 4 and fosfomycin in 1). The dose of ceftriaxone was 1 to 2 g per day in 28 cases, 3 g per day in 1 case (meningitis with abscess of the brain) and 1 g every other day in 1 case (chronic renal failure under hemodialysis). Duration of treatment ranged from 10 to 62 days (average 17 days). The usual routes of administration were IV and IM; the SC route was used on 4 occasions. Pharmacokinetic studies of serum levels were carried out in several patients including two who had ceftriaxone subcutaneously; results were consistent with those previously reported in the literature.(ABSTRACT TRUNCATED AT 250 WORDS)