We have observed three forms of skin toxicity induced by the new antifol trimetrexate in a Phase I trial. They are: radiation recall, cellulitis at the infusion site, and generalized skin eruptions with erythroderma. A total of 25 episodes of some form of skin reaction occurred in 31 patients. The generalized eruption began about four days after drug administration and cleared within a week. The mechanism of skin toxicity of trimetrexate and other antifols is unknown.