Summary In summary it may be said that penicillin holds definite promise as a therapeutic agent in yaws. Its use in doses of 1,200,000 O. U. in adults and proportionate doses for children given over periods of four, two and one days respectively resulted in rapid clinical cures. The serologic response was not as striking as the clinical, but until more follow-up figures are obtained a full evaluation is n ot possible. The oil-beeswax preparation of penicillin made it possible to treat patients on an ambulatory basis over one and two days with the same dose of penicillin given in aqueous solution to hospitalized patients over four days. The immediate clinical and serologic results obtained with pencillin in oil with beeswax appeared to be as good as those of the aqueous solution. The development of a successful one-day treatment schedule would be of great practical value in a country such as Haiti where large numbers of patients must be treated on an ambulatory basis in rural clinics. A report on 12 months follow-up observations will be made at a later date.