The effectiveness of intralesional bleomycin (1 U/ml) in the treatment of warts refractory to conventional methods of treatment has been shown in well-controlled studies. We have now evaluated more dilute concentrations of bleomycin in the treatment of recalcitrant warts. Warts were assigned for therapy with intralesional bleomycin at a concentration of 0.25 U/ml, 0.5 U/ml, or 1 U/ml at 3-week intervals. If warts persisted after three injections or had recurred by 3 months' follow-up, treatment was considered a failure. Twenty-six patients whose warts had persisted after conventional treatment entered the study. Three patients had spontaneous regression of untreated warts during therapy and were not included in the results. Of seventy-nine warts treated with intralesional bleomycin, sixty-two (78%) were cured after one to three injections. Responding warts showed a hemorrhagic eschar even with the lower bleomycin concentrations and healed without complication. Almost all treated warts responded, although not all were cured. Treatment with bleomycin at 0.5 U/ml was as effective as treatment with 1 U/ml. Bleomycin at 0.25 U/ml is effective therapy but not enough warts were treated to permit a conclusion when compared with higher concentrations.