A 69-year-old man presented with annular lichen planus involving both forearms, hand dorsa, wrists, inner sides of the thighs, knees and ankles. He was treated initially with systemic corticosteroids and etretinate, but rernission and recurr ence of the skin lesions were observed. During the follow-up, we found erythrasma on all his toewebs and both soles. After administration of erythromycin for the treatment of erythrasma, lesions of the lichen planus rapidly improved. Five months later, some lesions of lihen planus and erythrasma had recurred. After administration of erythromycin, the lesions of lichen planus improved again. No recurrence was observed for the following 8 months. We suspect that eradication of the chronic focus of infection and the anti-inflammatory effect, of erythromycin may lead to supression of abnormal immunological reactions and resolution of lichen planus. (Kor J Dermatol 1997;35(2): 307-311)