Using the avidin-biotin-peroxidase complex(ABC) technique, 36 skin specimens from 30 patients with primary and secondary syphilis and a gastric mucosal specimen from a patient with secondary syphilis which were confirmed by clinical history, physical examination, the VDRL, FTA-ABS, TPHA, and 19s(IgM)-FTA test, were examined. The results were compared with that of the indirect mmunoperoxidase technique which was done by authors previously with same specimens. The following results were obtained. 1. Of the 37 specimens, 35(95%) were positive in ABC technique and 33 of the 37 specirnens(89%) were positive in the indirect immunoperoxidase technique. 2. The ratio of agreement of the results between the ABC and the indirect immunoperoxidase technique was 89%. 3. Most of the treponemes were located in the upper dermis, epidermis, and blood vessel walls in the arder named, and rarely in the lower dermis of the syphilitic skin lesions. There was no remarkable difference in histologic distribution of treponemes between the clinical stages and types of syphilitic skin lesions. :From the results, the ABC technique is considered to be an excellent method for detecting the treponemes in the suspected syphilitic lesions.