The transient dynamics of specific cell growth rate during bioconversion of hexavalent chromium (Cr+6) to trivalent chromium (Cr+3) has been studied covering both Cr+6 uninhibited and Cr+6 inhibited conditions in a batch contacting system. Suitable polyculture consortia necessary for this bioconversion have been isolated and purified from tannery waste. It is observed that above the Cr+6 concentration of 33 mg/dm(3), effect of Cr+6 inhibition on the specific cell growth rate is appreciably high. Detailed simulation and modeling work indicate that while Monod model equation is capable of describing the cell growth dynamics under Cr+6 uninhibited condition, the same can well be represented by Briggs-Haldane uncompetitive type model equation under Cr+6 inhibited condition. Since for the present system the difference in magnitudes of two intrinsic kinetic parameters, namely, Monod constant, K-S and the inhibition constant, K-i is not appreciably large, a unified transient specific cell growth dynamic equation has been presented.