To avoid surgery-related complications, intralesional OK-432 therapy was used in 23 patients with unresectable lymphangiomas (1986 through 1989). Total or near total shrinkage of the lesions, without serious complication, was noted in 10, marked shrinkage in 8, slight shrinkage in 3, and no response was noted in the remaining 2. Recurrence of the lesions has not been observed during follow-up (4 to 35 months). The side effects of OK-432 therapy were a fever for 2 to 3 days and a local inflammatory reaction lasting 3 to 5 days. The local inflammation did not cause any damage to the overlying skin and did not lead to scar formation. The results suggest that intralesional OK-432 therapy is effective for most unresectable lymphangiomas.