OBJECTIVE: To compare heat denaturation and acidification as immune complex dissociation (ICD) methods in adult HIV-1 infection and to increase the sensitivity by a signal-amplification-boosted HIV-1 p24 antigen enzyme-linked immunosorbent assay (ELISA). DESIGN: Prospective and retrospective blinded study of paired serum and plasma samples from 245 patients (112 of class A, 66 of B, 67 of C of the Centers for Disease Control and Prevention 1993 classification). METHODS: Plasma and sera were prospectively tested for antigen by ELISA using native, acidified, or heat-denatured material. Retrospective tests included batch analysis of heat-denatured samples for antigen by the signal-amplification-boosted ELISA and for viral RNA. RESULTS: With serum, native antigen was reactive in 26.5%. Acidification increased the rate to 53.1% (P < or = 0.0001), but was inefficient at a CD4+ count > or = 500 x 10(6)/l. Heat denaturation further elevated the rate to 67.8% (P < or = 0.0007) and the use of plasma to 78.0% (P < or = 0.008). The boosted ELISA, performed with plasma samples diluted 1 :6, which eliminated the problem of heat-induced sample coagulation, was confirmed positive in 89.5% of serum and 97.8% of plasma samples. RNA was detected in 95.7%. CONCLUSION: Heat-mediated ICD combined with a signal-amplification-boosted ELISA detects HIV-1 expression as sensitively as a polymerase chain reaction kit for viral RNA, but at only a fraction of the cost. The procedure uses a 50 microliters plasma sample and should be fully automatable.