Of 259 predominately elderly male patients, with a positive serologic test for syphilis, 162 had negative Treponema Pallidum Immobilization tests and were therefore biological false-positive (BFP) reactors. This represents a prevalence of BFP reactions which is 65 times greater than that found in the general population. There was no increased prevalence of collagen-vascular disease among elderly male BFP reactors. Venereal history was not helpful in differentiating the syphilitic from the BFP reactor. The physician was unable to differentiate accurately the latent luetic from the BFP reactor without aid of a specific treponemal antigen test.