Different physiological groups of microorganisms; cellulolytics, xylanolytics, pectinolytics, proteolytics, lipolytics and methanogens were enumerated and monitored during the anaerobic digestion of tomato-processing waste (TPW). In the batch digestion lasting 110 days, the numbers of cellulolytics, xylanolytics, pectinolytics, proteolytics and lipolytics showed a steady increase up to 40 days, but declined thereafter. In the semicontinuous digestion, the numbers of cellulolytics, proteolytics and lipolytics were found to be greater at 24 and 32 days hydraulic retention times (HRT) than at 8 and 16 days HRT. On the other hand, the numbers of xylanolytics and pectinolytics varied very little at different HRT. At the higher HRT, there were more methanogens than at the lower HRT. Differences in the types of bacteria isolated from digesters in the batch and semicontinuous processes were found. Bacteria belonging to Bacteroides, Eubacteria, Fusobacteria, Lactobacillus, Propionibacteria and Selenomonas were isolated. Two apparently novel isolates of cellulolytic bacteria belonging to the genus Eubacteria were also found.