To evaluate the concentration of circulating RNA (viraemia) in patients with symptomatic primary HIV infection and relate it to sero-immunological parameters. Semiquantitation of circulating HIV RNA and proviral HIV DNA was performed using the polymerase chain reaction. Circulating HIV RNA concentrations were expressed as virus equivalent (RNA copies/2) per ml serum. The mean CD4+ lymphocyte count for 19 patients with symptomatic primary HIV infection was 583 x 10(6)/l. Fifteen (79%) patients had detectable levels of p24 antigen (median 462 pg/ml). Circulating HIV RNA (median 2.3 x 10(7) virus equivalent/ml serum) and proviral HIV DNA (median 3630 copies/ml blood) were detected in all samples tested. Follow-up data for five patients (200-1600 days) showed a 1-3 log reduction in circulating RNA within 2 months. Later, circulating RNA concentrations were consistently greater than 10(3) virus equivalent/ml serum. Within 10 days no p24 antigen was detectable. Levels of CD4+ cells varied markedly from patient to patient during the follow-up and, in this small group, no evident correlation was observed between circulating RNA levels and CD4+ lymphocyte counts. High concentrations of circulating RNA (viraemia) were present in 19 patients with symptomatic primary HIV infection. Although a decrease in viraemia was observed during the following 2 months, viraemia persisted in all patients with long-term follow-up. This suggests that active viral replication is a continuous process in HIV-infected patients.