Chronic venous leg ulcers are a common ailment with no ideal treatment. Recent reports have shown granulocyte- macrophage colony stimulating factor to be of use in the healing of these chronic wounds. Therefore, we conducted a double-blind, randomized, placebo-controlled study which enrolled 60 patients with chronic venous leg ulcers, whom we treated with placebo or with 200 or 400 microg of granulocyte-macrophage colony stimulating factor by perilesional injections of the drug in four weekly treatment episodes. Observations were conducted at each treatment visit, at weeks 5, 9, 13, and six months after the inclusion in the protocol. The number of healed wounds in the placebo and the treated arms were significantly different (p = 0.05), with 4 of 21 (19%) in the first group having healed at week 13, as compared to 12 of 21 (57%) and 11 of 18 (61%), in the 200 microg and the 400 microg groups, respectively. There were only minor side-effects attributable to the treatment, and the reobservation at 6 months showed that none of the treated ulcers recurred during that period. We conclude that granulocyte-macrophage colony stimulating factor injected perilesionally may be a useful drug for the treatment of chronic venous leg ulcers.