The authors examined 984 human sera for leptospirosis with the serovars from 15 serogroups serologically in 15 localities of El Salvador. In 17.5% of the sera the following reactions were found with serovars of 13 serogroups: Australis 6.8%, Pomona 5.5%, Grippotyphosa 3.2%, Icterohaemorrhagiae and Tarassovi each 2.1%, Javanica, Canicola, Pyrogenes, Cynopteri, Autumnalis, Sejroe, Hebdomadis, Bataviae, Shermani, between 0.2%-1.4%. Men showed a 18.5% and women 17.0% positive reaction. Positivity increases with an increase in age, an increase was shown from 11.5% in the group of up to 10 years, to 40.4% in the group of 51 to 60 years, in the last age group of over 60 years a decrease was shown of 34.7%. In 8 localities we were able to compare the serological positivity of the population, the highest percentages were found in Fey Esperanza 35.1%, San Jose de la Montana 31.6% and Domus Maria 27.8%, the lowest in Credisa 6.4% and Ametepec 7.6%.