Stability-indicative determination of meropenem (MERM) in the presence of its open-ring degradation product, the metabolite, is investigated. The degradation product has been isolated, via acid-degradation, characterized and confirmed. Selective quantification of MERM, singly in bulk form, pharmaceutical formulations and/or in the presence of its major degradate is demonstrated. The indication of stability has been undertaken under conditions likely to be expected at normal storage. Among the analytical techniques adopted for quantification are spectrophotometry [first-derivative ((1)D), first-derivative of ratio spectra ((1)DD) and bivariate analysis], as well as chromatography [coupled TLC-densitometry and HPLC].