Production of herpes simplex virus (HSV)-specific interferon- gamma by peripheral-blood mononuclear cells (PBMCs) of HSV-seropositive healthy donors and human immunodeficiency virus-infected persons was determined by use of ELISPOT. The mean +/- SD number of spot-forming cells/10(6) PBMCs was 314 +/- 74 in 11 healthy donors, 360 +/- 69 in 3 long-term nonprogressors (LTNPs), 186 +/- 52 in 9 newly diagnosed patients, and 181 +/- 59 in 33 patients who were receiving highly active antiretroviral therapy (HAART) for a median period of 30 months (range, 1-109 months). In 9 patients monitored prospectively while receiving virologically and immunologically successful first-line HAART, the number of spot-forming cells increased by 5.6/month (95% confidence interval, 1.2-9.9 [P=.01]) and 21.3/100 CD4 cells/mm(3) gained (95% confidence interval, 13.8-28.7 [P<.0001]). Responses were correlated with LTNP status and CD4 cell count.