ACV is an effective agent for the treatment and prophylaxis of HSV infections in both IC and immunologically normal individuals. The drug is well tolerated in both populations and is not significantly associated with clinical or laboratory toxicities. Because of the great potential benefit and low risk, organ transplant recipients and patients with hematologic malignancies undergoing induction chemotherapy should be screened routinely for HSV antibodies; seropositive individuals should receive prophylactic ACV during the period of most profound immunosuppression. Immunologically normal individuals with frequently recurring genital HSV or serious complications associated with outbreaks are candidates for long-term suppression with ACV.