Mucocutaneous herpes simplex virus (HSV) infections that are resistant to therapy with acyclovir have been recognized with increasing frequency in patients with the acquired immunodeficiency syndrome, although alternative therapies in this setting have not been widely studied. Twenty-six consecutive patients are reported with human immunodeficiency virus infection, who received foscarnet therapy for acyclovir-resistant HSV. Clinical response was noted in 81% of patients; complete reepithelialization of HSV lesions occurred in 73%. Cessation of viral shedding was documented in all of the 11 patients who were recultured. Although adverse effects were frequent, in only 3 patients (12%) did toxicity necessitate discontinuation of therapy. Before foscarnet therapy, 14 patients received vidarabine for acyclovir-resistant HSV. The infection did not resolve in any of the vidarabine-treated patients, and therapy was discontinued in 4 (29%) due to toxicity.