Four laboratory-scale anaerobic digesters were deliberately and completely inhibited by feeding sodium oleate to such an extent that no methane was produced from the digesters. Three of them were then respectively fed glucose, cysteine or glucose and cysteine along with sodium oleate, while the remaining digester was operated as control reactor and continued to be fed with only sodium oleate. Oligonucleotide probes ARC915, EUB338, MB310, MC1109, MSMX860 and MG1200 were used to target and quantify specific groups of microbes, Archaea, Bacteria, Methanobacteriales, Methanococcales, Methanosarcinaceae, and Methanomicrobiaceae, Methanocorpusculaceae and Methanoplanaceae respectively throughout the operation of reactors. Addition of glucose and/or cysteine assisted with the recovery of methane production from oleate inhibition. The addition of glucose was more effective than cysteine, while the combination of glucose and cysteine was most effective on this recovery. The addition of these substrates also stimulated the degradation of oleate in the reactor. Daily methane production from the digesters correlated negatively with residual oleate concentration and positively with Archaea counts. Addition of glucose was more effective than cysteine on increasing the number of Archaea cells, while cysteine was more effective in increasing the number of Bacteria cells. All microbial populations recovered to pre-inhibition levels within 40 days when glucose together with cysteine was fed. (c) 2006 Society of Chemical Industry.