Determination of antibodies to HIV virus by the ELISA technique was performed in 27,652 serum samples from January 1988 to November 1989. Samples which were positive twice underwent the Western Blot technique. A 0.41% of positiveness to the virus was found in 1988 and a 0.34% in 1989. Confirmation of positive cases by Western Blot was statistically significant in 1989.