In this paper, the valoration bioassays for ceftriaxone, cefotaxime, ceftazidime, ampiciline/sulbactam and imipene/cilastatine were developed. Only one microorganism (Bacillus subtilis ATCC 66 33 spores) was established to perform the bioassay. The concentration range that has the better correlation doses - answer is characteristic of each antibiotic, like the bioassay conditions (antibiotic solitions pH, media culture pH, incubation time). A comparative study of samples from generic, innovating and trade marck productos of theses antibiotics, with the validated bioassays, shown that all the samples have the same antimicrobial activity in vitro, and confirm that they are pharmaceutical equivalents.