Twenty-four biopsy specimens of skin were taken from 23 patients with several types of lesions of secondary syphilis. In macular and maculopapular lesions, the histological changes were not specific. No or few plasma cells were observed in specimens at this stage. In early papular lesions, the histological appearance was more diagnostic. A lymphohistiocytic bandlike infiltrate was present in the upper part of the dermis and extended around blood vessels of the deep plexus. In nearly two-thirds of the cases, plasma cells were present in early papular lesions. The epidermis, too, was frequently involved in these lesions of the disease. In late papular lesions, the pathologic features were distinctive. The infiltrate was dense, diffuse, and, in some instances, nearly completely plasmocytic. In nummular syphilides, many neutrophils were present in a hyperplastic epidermis, whereas in corymbiform lesions, the epidermis was not involved at all.