The aim of the study was to determine the prevalence of selective lactose malabsorption (SLM) in Khants, a small finno-ugric nation living in West Siberia. A total of 80 Khants from the Surgut region (Tyumen territory) were studied. The diagnosis of SLM was based on the evidence obtained at a 50 g lactose and, if possible, a 25 g + 25 g galactose-glucose loads. In 6 cases electron-microscopic examination of the duodenal mucosa was performed. The prevalence of SLM in the Khants reached 93-94% being the highest in CIS.