BRL 42715 is a new penem which inhibits a wide range of plasmid as well as chromosomally mediated bacterial beta-lactamases. We used a total of 902 recent clinical isolates, consisting of 455 Enterobacteriaceae, 247 staphylococci and 200 other gram-negative bacteria to evaluate its ability for potentiation of amoxycillin. MICs for all the 104 strains of methicillin-susceptible Staphylococcus aureus were reduced from 8-greater than 32.0 to less than or equal to 0.06 micrograms/ml in the presence of 1-5 micrograms/ml of this penem. It was also highly effective in inhibiting the beta-lactamase of a wide variety of gram-negative bacteria, thereby bringing their MIC values for amoxycillin from a 'resistant' range (greater than 32.0 micrograms/ml) to a 'susceptible' range (less than or equal to 8.0 micrograms/ml). Commonly resistant bacteria like Klebsiella, Enterobacter, Citrobacter, Morganella, Serratia, Acinetobacter and Aeromonas were rendered susceptible to amoxycillin in the presence of 1.0-5.0 micrograms/ml of BRL 42715.