The paper deals with observations of the patients with non-A-non-B hepatitis (NANBH) transmitted by the fecal-oral mode. The disease was diagnosed by ruling out other similar diseases of the liver, primarily viral A (HA) and B (HB) hepatitides, using clinical and epidemiological data and highly sensitive methods of laboratory diagnosis of HA and HB. Cases of NANBH occurred in one of Central Asia regions in the period of the usual seasonal rise of incidence. The disease was more frequent in adults, running a mild course in most patients, although there were also severe forms with fatal outcomes observed only in pregnant women in the second half of pregnancy. The lethality among the pregnant women was 15.7%. Immune electron microscopy of fecal specimens collected from the patients in the early days of jaundice revealed virus-like particles of 27-30 nm in diameter, morphologically similar to HA virus but forming no immune complexes upon treatment with blood sera containing antibody to HA virus antigen.