The physicochemical equivalencies of drugs are not usually correlate to the generic equivalencies of drugs and the generic equivalencies of drugs produced by different manufacturers or different formulations are being called in question frequently. The bioabailability of two formulations of oxytetracycline and erythromycin stearate were performed in healthy human volunteers. At the same time, the disintegration testes were performed with randomly sampled materials in question. For the biological evaluation of new oxytetracycline formulation; tablet(250mg), two-way cross over study in 10 healthy young volunteers was performed using oxytetracycline capsule (250mg) as reference, Erythromycin stearate (250mg) tablets and capsules produced by different manufacturers were compared in a two-way cross over study in 12 subjects with same manner of oxytetracyclines. oxytetracycline tablets showed somewhat slow disintegration rate, but appeared not statistical differences in serum concentrations from the reference, up to six hours after ingestion. Erythromycin stearate capsules disintegrated more rapidly than enteric coated tablets. Serum concentrations of capsules were more variable and markedly lower (P<.005 after 2hrs) than the enteric coated tablets. Rapid disintegration of capsules may result in destruction of active chemicals owing to the interaction with gastric acid and the above factor may contribute mainly to the low serum level after ingestion of capsules.