A focus of microfilariasis was detected in El Oculto, Orán Department, 300 km northern from Salta city. These results prove the prevalence of this parasitosis in Argentina, despite the lack of cases registered during the last 35 years. The incidence detected was 20.7%; similar values were reported in 1917 by Biglieri and Aráoz in a wooded area located in the oriental face of Aconquija mountain, in Tucuman province, approximately 600 km southern from El Oculto. The results presented suggest the interruption in the transmission of this parasitosis.