Eleven patients, 8 females and 3 males, aged 17-53 years with chronic recurrent pyoderma (mean duration of 8.4 years) unresponsive to a variety of therapeutic modalities, were treated with oral levamisole 1 . 5-2 . 5 mg/kg/day (100-200 mg daily) for 2 consecutive days every week. Five out of eleven patients (3 males and 2 females) demonstrated one or more host defense abnormalities including impaired polymorphonuclear (PMN) chemotaxis, impaired bactericidal activity against Staphylococcus aureus, decreased in vitro lymphocyte response to Phytohaemagglutinin (PHA) and low serum IgM and IgA. Seven of eleven patients showed clinical improvement following levamisole administration for 4-11 months. Two showed complete clearance of skin lesions while on levamisole and for a year thereafter; three showed marked clearance of lesions during levamisole therapy but recurred with mild disease 6 months after termination of levamisole therapy; and two showed improvement of lesions during therapy but recurred immediately after levamisole discontinuation. Levamisole treatment was also associated with complete in vitro correction of PMN bactericidal abnormality, improvement of PMN chemotactic abnormality and augmentation of in vitro lymphocyte response to PHA. Correlation between in vitro potentiation of host defense mechanisms and clinical response was noted. Significant probable side-effects necessitating discontinuation of therapy included transient elevation of liver enzymes in 2 patients and extensive hemorrhagic skin rash in one.