The in vitro determination of the T log and the minimal bactericidal time of cefatrizine was evaluated against H. influenzae, Str. pyogenes A isolated from clinical specimens. and K. pneumonia ATCC 10031 and compared with that of amoxycillin, cefaclor, cefroxadine and miocamycin against the same bacterial strains. Cefatrizine demonstrate the shorter TMB against all bacterial strains and antibiotic tested with MBCs.