Paper presents the RIHA and EIA data of an annual 3-year survey of populations of two reindeer breeders' settlements in the Nenets Autonomous Okrug of Arkhangelsk Province with the use of intact Echinococcus antigen (RIHA) and fractions of Echinococcus multilocularis antigens (EIA). In 1984-1986, seropositivity has been established by 2 immunoassays for 98 (21.6 +/- 1.9%) out of 454 apparently healthy subjects. The annual Echinococcus invasion rate in population varied within 2.8-3.7%, as estimated by RIHA, and 4.6-4.8%, according to EIA data. The highest invasion rate was observed among the those engaged in reindeer breeding, hunting, animal breeding as well as among the aboriginal populations the Nentsi and the Komi.