The immune responses to varicella zoster virus were studied in 67 otherwise normal children participating in a placebo-controlled trial of acyclovir for the treatment of chickenpox. No differences were observed between acyclovir and placebo groups. Children were studied longitudinally, at onset of chickenpox, and at 1 month, 3 months, 1 year, and 3 years after infection. These data help define the natural history of the immune response to chickenpox in children.