This paper reports the results of in vitro anti-bacterial activities of piperacillin against 430 strains of pathogens isolated clinically and compares with those of five cephalosporins. The resuIts indicate that piperacillin is a broad spectrum semisynthetic penicillin.It is active against gram-positive cocci and gram-negative organisms. The antibacterial activity against gram-positive cocci

of piperacillin is less than those of the first and the second generation cephalosporins

but is more active than those of the third generation cephalosporins; while the reverse was true against Gram-negative Enterobacteriaceae. However

ceftazidime and piperacillin are the most active two than others against Pseudomonas aeruginosa. Piperacillin also shows good antibacterial activities against enterococci and Acinetobacter which the cephalosporins do not possess