A herd of Mexican Hairless Swine, maintained in an agro-silvi-culture pasture in the village of Chapa de Mota, Mexico, underwent a serological study after one of the sows aborted a litter showing fever. Blood samples were drawn from thirty-four animals in reproductive stage, which then underwent a treatment, based on a streptomycin dose of 25 mg/kg live weight during five days. Twenty-eight samples were taken 15 days after the herd either farrowed or aborted. Seroconversion was found in five animals with a serovar of hardjo H 89 origin. One of the animals aborted after seventy-eight days of gestation; in all the cases there was a negative increase of between 1:200 to 1:800 titres, while the serovar bratislava presented titres in six animals. In two cases the seroconversion went from a negative to a 1:200, while one of the pigs miscarried on the 77th day of pregnancy, and two other animals went from a titre 1:100 to 1:200. Another sow lost a litter on day 84, and in the last two animals the titre was maintained at 1:100, though one of the pigs aborted on the 86th day. This paper constitutes the first report of an outbreak of abortions in the Mexican Hairless Swine caused by Leptospira interrogans serovars bratislava and hardjo.