We developed an enzyme-linked immunosorbent assay (ELISA) for measuring the antibody response to herpes simplex virus (HSV) glycoprotein D (gD). The ELISA was specific and more sensitive than immunoblotting techniques. Antibody to HSV gD was detected in 10of 12sera (geometric mean titer, 36.3) obtained from HSV-2-infected guinea pigs 14 days after intravaginal inoculation, and the titer increased to ⩾5,120 on day 60. Therapy with acyclovir delayed and diminished the antibody response to gD, although by day 60 the titers of antibody to gD in acyclovir-treated animals were not significantly different from those in controls. An increased titer of antibody to gD seemed to be associated with a reduced number of recurrent episodes and to a reduced number of days with recurrent lesions. © 1987 by The University of Chicago.