The number of human immunodeficiency virus (HIV) DNA copies in peripheral blood mononuclear cells (PBMC) was quantitated by the polymerase chain reaction (PCR) and used as a virologic marker in a clinical trial with beta-interferon (beta-IFN) (6 x 10(6) IU/day administered intravenously for 4 weeks). In 11 HIV-infected patients who were clinically stable, the number ranged from 10 to 1,063 copies per 10(5) PBMC. However, percent change of the number in the individual untreated patients stayed between -46.2% and 203.0% of the basal level by one month interval. In six patients who were treated with beta-IFN, changes in the number were not significant before and after the trial.