Abstract Amoebic antigen prepared from axenic Entamoeba histolytica (NIH:200 strain) grown at 37 °C in TPS I medium was chromatographed on a Sephadex G-200 column. Three fractions (F-I, F-II, F-III) were obtained, the molecular weights of which ranged from 650,000 to 1,450. Fractions were concentrated by lyophilization and antisera against each fraction and whole antigen were raised in rabbits. Partially purified fractions were used in various serological tests and their reactivities were compared with whole amoebic antigen. Main haemagglutinating and precipitating activities were confined to Fraction I, which had 14% of total protein and the highest molecular weight (650,000). 5 μg/ml of protein contained in this fraction gave antibody titres comparable to those obtained with whole antigen with 40μg/ml of protein. Other fractions, although they had precipitin activity, lacked haemagglutinating activity. The protective efficacies of these fractions are being investigated in our laboratory.