To assess the response and toxicity of liquid nitrogen cryotherapy for cutaneous lesions of Kaposi's sarcoma (KS) associated with AIDS, we evaluated 20 subjects with biopsy-proven KS in a phase II clinical trial. Subjects had two to four cutaneous KS indicator lesions treated with liquid nitrogen cyrotherapy. Treatment was repeated at 3 week intervals, allowing adequate healing time. On average, subjects received three treatments per lesion with a mean follow-up time of 11 weeks (range of 6-25 weeks). One treatment consisted of two freeze-thaw cycles, with thaw times ranging from 11 to 60 s per cycle. A complete response was observed in 80% of treated KS lesions and lasted a minimum of 6 weeks following the completion of therapy. Greater than 50% cosmetic improvement of KS was observed. Histopathology of treated lesions correlated poorly with cosmetic improvement. Response was not predicted by tolerance to zidovudine therapy, CD4+ cell count, presence of B symptoms, or previous chemotherapy. Subjects without prior history of opportunistic infection (OI) were more likely to have a better response than those with a prior history of OI. Subjects tolerated cryotherapy well. Blistering occurred frequently, but local pain was limited and relieved by acetaminophen. Secondary infection did not occur. Based on this study, we recommend cryotherapy to subjects with cutaneous KS lesions. Liquid nitrogen cryotherapy is easily applied as a primary therapy, and may also have a role in the treatment of cutaneous KS lesions that respond slowly or show incomplete cosmetic improvement with systemic therapies.