objective: to evaluate the sensitivity and specificity of the polymerase chain reaction (pcr), enzyme-linked immunosorbent assay (elisa) and iga-specific immunoblot assays as ancillary methods to diagnose human immunodeficiency virus (hiv-1) perinatal infection. material and methods: a comparative study was conducted between february and october 2001 at the human retrovirus research unit of mexico's national university. ninety infected and 153 non-infected children were included in the study. viral cultures were the gold standard tests. standardized pcr for a conserved region of the gag gene and hiv-specific iga antibody using elisa and immunoblot were used. statistical analysis of results was performed with spss 10.0. results: iga elisa sensitivity and specificity were 61.1% and 90.8%, respectively. immunoblot had a sensitivity of 82.2% and a specificity of 95.4%. pcr had an overall sensitivity of 98.3% and a specificity of 100% with only one false negative result. if both assays were run, the sensitivity increased to 100% and the specificity to 96%. conclusions: a very high sensitivity and specificity is reached when using together pcr and iga immunoblot; these assays are useful for perinatal diagnosis of hiv-1.