The antileukemic agent cytarabine has recently been used to treat herpesvirus infections, but the regimens advocated for this purpose are high-dose prolonged infusions (100 mg/sq m of body surface per day for five days). The use of cytarabine as an antiviral agent has been restricted by the toxic effects produced with these regimens. We have treated ten patients with herpesvirus infections of wide range of severity using cytarabine infusions ranging from 10 to 100 mg/sq m /day for 1 1/2 to 7 days. In each case, the viral infection responded favorably soon after cytarabine therapy was started, even when low doses were given for short periods. The low-dose short-period infusions produced few toxic effects. Thus, cytarabine may be more useful as an antiviral agent than has previously been realized. Controlled studies are required to confirm this clinical impression.