Entamoeba polecki Prowazek, 1912 was recorded for the first time in Czechoslovakia in two students from Kampuchea. Uninucleated cysts of diameter 14.2-15.7 micron with nuclei diameter 3.2-4.2 micron were found-repeatedly in stool samples taken from them. The nucleus accounted in average for 24.3% of the cyst diameter. The isolation and two following subinoculations on Dobell-Leidlaw medium were achieved, more abundant growth was recorded on medium with pig serum. Sera of both students were positive in serological tests using the E. histolytica antigen. No serious clinical symptoms were observed, both patients were cured successfully by metronidazole and ornidazole. Electroimmunotransfer blots were used to characterize E. polecki as a separate species. The antigenic structure of polyxenically grown E. polecki was compared with the antigenic structure of E. histolytica (axenically grown HK-9 strain and 3 polyxenically grown strains). Different blot patterns of both species were obtained, but common fractions of 30-40 kD probably responsible for serological cross-reactions were found.