Search for natural foci of leptospirosis was carried out in 1987-1989 in humid biotopes of Tashauz Province, Turkmenistan. Such potential carriers of leptospirosis as house mice (Mus musculus) and tamarisk gerbils (Meriones tamariscinus) are widely spread in this area, and the size of their population can amount to great numbers. The sharpest fluctuations in the population size are characteristic of house mice inhabiting the shores of water collecting ponds and lakes in the regions of minimally used pastures. A moderate number of house mice was registered in spring and autumn at the area of irrigated agriculture. Only here and only in autumn a faint epizootic manifestation of the natural focus of L. grippotyphosa infection in house mice was registered for the first time in Turkmenistan. The titers in mouse blood sera, determined in the microagglutination test and the Leptospira lysis test, were 1:20 to 1:200. According to the data on the humidity and pH of the soil in the vicinity of irrigated fields, spring and summer months may be regarded as the most favorable period for the survival of leptospires in the environment. The probability of the aggravation of the epizootic situation seems to increase when irrigated fields adjoin pastures of are temporarily used as grazing ground for cattle.