Drinking water denitrification was studied on a membrane bioreactor pilot plant. The nitrate removal yields remained constant at 99 %. The specific denitrification activities averaged 0.16 kg N-NO3.kg−1MLSS.d−1 at 20°C and pH 8. The permeation flux was about 0.5 m3.m−2.d−1 throughout the study and did not vary with an increase in the suspended solids concentration. The dependence of the process efficiency on temperature and pH was put into equation. The specific denitrification activity decreased by a factor 1.9 with a temperature decrease of 10°C. The optimal pH was found to be 8 – 8.5. The ethanol consumption was 1.4 g C.g−1N-NO3. The membrane bioreactor technique seems to be a promising answer for the nitrate problem of drinking waters.