Disodium phosphonoacetate (PAA) in a cream-ointment base was applied to herpesvirus skin lesions on the genitalia of cebus monkeys. The lesions had been produced by the intradermal injection of herpes simplex virus type 2. Concentrations of 0.2, 2, and 5% PAA were used. Liberal application of PAA at concentrations of 2 and 5% proved extremely irritating and produced extensive, severe lesions over the treated area. The 2% PAA, when applied carefully to the lesion area, proved less irritating, but did not reduce healing time when compared with the placebo-treated animals. The 0.2% PAA caused slight reduction in lesion size and duration, but these differences were not statistically significant when compared with placebo-treated animals.