A new non-isotopic sandwich hybridization assay was developed to detect human immunodeficiency virus type 1 (HIV1) provirus amplified by the polymerase chain reaction. The sensitivity and specificity of this new technique using 96-well microplates as the support for the sandwich hybridization procedure and stable enzyme-linked oligomer as the detection probe were compared with those of Southern hybridization using a 32P-labelled oligomer probe. Three laboratories studied 437 peripheral blood mononuclear cell samples from 294 different subjects including both HIV1-seropositive and -seronegative individuals. The non-isotopic assay exhibited a sensitivity of 99.5% and a specificity of 99.1% when compared with the Southern procedure. In addition, the non-isotopic assay gives clear numeric data, is safe when handling, and is especially adapted to large-scale analyses.