Fifty immunocompromised children with varicella who exhibited no signs of dissemination were treated with intravenous acyclovir or placebo in a double-blind, randomized study. Twelve of 25 placebo recipients were withdrawn from treatment because of their deteriorating condition and were given open acyclovir therapy; only one of 25 recipients of acyclovir was similarly withdrawn (P < .001). Among those patients who did not receive open treatment, acyclovir significantly reduced time to full crusting (P = .01). Overall, acyclovir, as judged by the physician, significantly improved the patients' condition.