The paper outlines results of the experimental assessment of nitrification kinetics applicable to tannery wastewaters and thr inhibitory effects of selected pollutants on nitrification. The average net growth rate of nitrifiers was measured as 0.32 d(-1) at 20 degrees C and 0.10 d(-1) at 10 degrees C for tannery wastewaters subjected to plain settling. This: kinetic coefficient was observed to increase to 0.43 d(-1) at 20 degrees C with chemical settling. Parallel experiments with synthetic waste containing only NH4Cl revealed the strong inhibitory character of tannery wastewater. Chromium was observed to be partly responsible for the inhibitory effect which was mainly induced by chloride, inherently present in this type of wastewaters.