In the present study, we attempted to purify herpes simplex virus (HSV) tumor associated antigen(s) (TAA) extracted from human kidney carcinoma. Trypsinized human tumor cells were sonicated for 9 minutes and clarified at 100,000 x g for 1 hour; the supernate yielded 70% of detectable TAA as determined by means of quantitative absorption with specific antisera. The supernate used as source of soluble HSV-TAA was concentrated and the pellet was resuspended in 0.02 M tris, pH 7.2, and purified by means of filtration on Sephadex G-100 followed by chromatography on DEAE Sephadex A-50 and then affinity chromatography on concanavalin A (Con A) sepharose. The TAA bound to Con A sepharose was eluted by 0.5 M of alpha-CH3D-mannoside (alpha-MM) and behaved as a glycoprotein. The molecular weight determined on SDS-PAGE was about 70,000 daltons in relation to standard marker proteins. This antigen reacted in complement fixing tests with hyperimmune guinea pig sera as well as with certain human squamous cancer sera. As a control we used a human kidney carcinoma which showed no complement fixing activity in any of the procedural steps, and as control sera, guinea pig sera prepared by inoculation of uninfected guinea pig cells.