Phenolic wastewater representing an industrial wastewater was supplemented with varying amount of nitrogen (N) and phosphorous (P) and treated in upflow anaerobic sludge blanket reactor (IJASBR). The variation of COD:N:P from 300:10:1 to 300:1:0.1, did not influence the conversion of phenol COD to methane COD. The concentration of N and P in the influent was reduced from 25.5 mg l(-1) to 2.5 mg l(-1) and 2.5 to 0.25 mg l(-1), respectively. However, on further reducing the nutrients in the feed from 300:1:0.1 to 300:0:0 the (i) CH4-COD decreased from 90% to 40%, and (ii) cell yield reduced to 25-50%. The average cell yield was 3.5%. Percent N and P in cells varied from 10% to 14% and 0.6% to 2.4%, respectively. The activity of the sludge assessed as specific methanogenic activity (SMA) was found in the range from 0.15 to 0.66g CH4-COD g(-1) VSS d(-1). The optimum COD:N:P for phenolic wastewater has been estimated to be 300:1:0.1. (c) 2008 Elsevier Ltd. All rights reserved.