The yeast Kluyveromyces marxianus has been shown to be a potential source of endopolygalacturonase for use in the food industry. However, uncertainty exists in the nature and spectrum of the enzymes secreted. In this study, four forms of endopolygalacturonase (1,4-α-d-galacosiduronate glycanohydrolase, EC 3.2.1.15) were isolated from the culture fluid of K. marxianus, strain NCYC 587. SDS polyacrylamide gel electrophoresis indicated that three of the isoenzymes had an Mr of 49,600 and one of 46,700. The amino acid content of the isoenzymes was very similar and they all cross reacted strongly with antibodies raised against one of the purified enzymes. All the endopolygalacturonases were glycoproteins, the neutral sugar content varying between 2.3% and 13.8%. © 1990.