A simple, rapid, reproducible and sensitive peptide-Time-Resolved-Fluoroimmunoassay (TR-FIA) method is described which allows the detection of antibodies to the Human Immunodeficiency Virus type 1 (HIV-1). By using a panel of synthetic peptide antigens that covered env, gag and pol amino acid sequences, a 20 amino acid peptide (GIWGCSGKLICTTAVPWNAS) describing an immunodominant and conserved domain on the gp41 region of the BH10 clone was found to be the most reactive in this study. Optimal conditions for antigen concentration, serum dilution and incubation time were established. The peptide-TR-FIA is specific, as assessed by testing HIV-1 positive sera which included samples from AIDS, ARC patients and HIV-positive drug users. The test was used to detect HIV antibodies in 250 well characterized HIV-1 positive sera and 50 normal sera. Peptide-TR-FIA results indicate that the env peptide was highly reactive with HIV-positive sera showing a sensitivity of 100%. None of the 50 control sera showed positive reactivity against the synthetic peptide. Furthermore the peptide-TR-FIA allowed a fine titration of antibodies to defined epitopes of immunodominant HIV structural proteins that usually cannot be achieved by peptide-ELISA assays.