Four strains of enterovirus and 1 strain of adenovirus were isolated from stool and pharyngeal swabs by inoculation into primary human embryonic kidney cell culture in 25 cases of dorsum manus infantile papular dermatitis. Two strains of Coxsackie A-9 virus and 1 strain of Echovirus-25 were identified. With the isolated virus as antigen, a matched pair study by sera antibody test was carried out in 43 children with papular dermatitis and 40 normal individuals as controls. In 26 cases of Coxsackie A-9 virus positive papular dermatitis, a 4-fold rise (> 1:1.6) in the relative serum antibody was observed in 80.77%, while no high levels were observed in patients with Echovirus-25 and adenovirus dermatitis (< 1:16). The authors can reasonably conclude that epidemic Coxsackie A-9 virus infection is obviously related to infantile papular dermatitis and is probably the main cause of the disease.