This paper firstly reviews the natural history of genital herpes, giving special attention to the differences between primary and non-primary initial disease and recurrent disease and between herpes simplex virus 1 and 2. Secondly, previous therapies for genital herpes, and in particular the problems associated with previous drug trials are considered. The final part of the paper reviews a double-blind placebo controlled randomized study of intravenous acyclovir in patients with severe first attack, genital herpes. Intravenous acyclovir significantly reduced the duration of viral shedding, the healing time, the duration of vesicles and new lesion formation, and the duration of all symptoms, but did not prevent subsequent recurrences.