Nine patients with cystic hygroma were treated with a new sclerosing therapy consisting of intracystic injection of OK-432 (group A Streptococcus pyogenes of human origin). Favourable results including complete regression in eight patients and marked regression in one were observed within 2-3 months without serious side-effects except for fever of 2-3 days' duration and local inflammatory reaction lasting for 3-4 days. Local inflammatory reaction did not cause any damage to the overlying skin and did not lead to scar formation.