The human parasite Entamoeba histolytica is an amitochondrial protozoan whose metabolism depends on glucose fermentation. Among the metabolic enzymes absolutely required for amoeba growth is the NAD(+)-dependent alcohol dehydrogenase (EhADH2). The polymeric form of EhADH2 was sedimented at 160,000g, and in this fraction we observed [P-32]-labeling of a 96-kDa protein under monoADP-ribosylation conditions with [P-32] NAD(+). The [P-32]-labeled protein had the same molecular weight as the EhADH2 monomer. Because of the importance of monoADP-ribosylation in the regulation of many physiological processes, the aim of this study was to determine whether EhADH2 is ADP-ribosylated, and what would be the consequence of this modification on its alcohol and aldehyde dehydrogenase enzymatic activities. This study describes the ADP-ribosylation of EhADH2. This modification did not have an effect on the enzymatic activities, but it may regulate other functions of EhADH2.