In this study, 63 patients with various urinary tract infections were treated with cefotaxime in different dosages. They were aged from 10 to 82 years (mean: 59). The cases included 33 cystitis, 25 pyelonephritis, 4 chronic prostatitis and 1 orchiepididymitis. 85 strains of enterobacteria were identified: 20 E. coli, 2 Citrobacter freundi, 5 Proteus mirabilis, 12 indole positive Proteus, 1 Providentia, 11 Klebsiella, 3 Enterobacter cloacae and 31 Serratia marescens and liquefaciens. 80 of these strains had MIC less than or equal to 1 mcg/ml (median: 0,12 mcg/ml). More than 2/3 of the patients were treated with a daily dose of 1.50 to 2 g, and 52 (median: 0.12 mcg/ml). More than 2/3 of the patients results showed 43 cures (9 of these with reinfection) and 20 relapses. Isolated enterobacteria strains were sensitive to cefotaxime in patients with recurrence. Relapses were due to underlying urological pathology. Among reinfection organisms, only one, an Enterobacter cloacae, was resistant to cefotaxime. The clinical, local, systemic and biological tolerance was good. Cefotaxime has been very effective in the treatment of severe urinary tract infections, especially in chronic pyelonephritis and cystitis, at an average daily dose of 2 g.