In order to establish the extent of paracoccidiodomicotic infection in a town at the southwest of Antioquia -where recently a case was informed- a descriptive research was carried out in San Mateo with a sample of 59 people, to whom skin tests with paracoccidioidin, histoplasminand tuberculin were applied following a codified schedule. Those individuals with positive paracoccidioidin test were further checked with serologic studies as complement fixation and immunodifusion in Agar-gel. The total percentage of positive paracoccidioidin testswas32%, primarily among men (39,4 %), farmers (54,5%) and peoplebetween35 and 50 year of age(58,3 %). The frecuency distribution of the size of reaction to paracoccidioidin pointed out the existence of specific reactions to the antigen. The presence of people who reacted to paracoccidioidin but did not to histoplasmin; the distribution of the size of reaction to paracoccidioidin; and the absence of specific antibodies to P. brasiliensis in the sera of those with positive paracoccidioidin skin tests, suggests the existence of an infection of beningn, asymptomatic course in some of the people of the studied area. The results obtained allows to conclude that this area is moderatelly endemic for paracoccidioidomicotic infection, but not for the disease.