We assessed the effect of acyclovir therapy on renal function during a course of therapy for herpesvirus disease. Renal function was assessed by measuring the clearances of inulin, albumin, and β2-microglobulin at the beginning and end of acyclovir therapy. Thirty-two patients had valid paired inulin clearances and 21 had valid paired albumin and (32-microglobulin clearances. No significant mean decrement of renal function was observed; however, 2 patients had a reversible renal dysfunction associated with acyclovir therapy which disappeared soon after discontinuation of the drug and was unassociated with a prior or recurrent renal dysfunction in short-term follow-up