Venlafaxine is a novel antidepressant, whichacts by inhibition of the reuptake of presynapticnoradrenalin and serotonin. In humans, it ismetabolized by CYP450 2D6 to an activemetabolite O-desmethyl venlafaxine, which hasantidepressant activity similar to that of parentdrug. Microorganisms have recently been successfullyused as models for drug metabolismstudies and for obtaining metabolites that couldbe developed as new drug entities. In the presentinvestigation venlafaxine was used for producingan active metabolite by microbial model usingdifferent microorganisms. For estimation ofvenlafaxine and its metabolites in microbialbiotransformation studies, a rapid, specific andsensitive HPLC method was developed.Linearity was observed over a concentrationrange of 0.5?g – 10?g/ml. Accuracy (98.15%)was achieved for all quality controls with intradayand inter-day variation coefficient less than8%. No endogenous interfering peaks werevisible with blank culture media. A metabolite peakwas found in the sample of Saccharomycescerevesiae culture among five organisms used.This method was used for estimation of thevenlafaxine metabolites in microbial biotransformationstudies.