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Clarithromycin (CLA) and roxithromycin (ROX) are macrolide antibiotics with an expanded spectrum of activity that are commercially available as tablets. A microbiological assay, applying the cylinder–plate method and using a strain of Micrococcus luteus ATCC 9341 as test organism, has been used and validated for the quantification of two macrolide drugs; CLA and ROX in pure and pharmaceutical formulations. The validation of the proposed method was carried out for linearity, precision, accuracy and specificity. The linear dynamic ranges were from 0.1 to 0.5 μg/mL for both compounds. Logarithmic calibration curve was obtained for each macrolide (r > 0.989) with statistically equal slopes varying from 3.275 to 4.038, and a percentage relative standard deviation in the range of 0.24–0.92%. Moreover, the method was applied successfully for the assay of the studied drugs in pharmaceutical tablet dosage forms. Recovery from standard addition experiments in commercial products was 94.71–96.91% regarding clarithromycin and 93.94–98.12% regarding roxithromycin, with a precision (%RSD) 1.32–2.11%. Accordingly, this microbiological assay can be used for routine quality control analysis of titled drugs in tablet formulations.