In the present investigation molecular components associated with the urines from bladder cancer patients and normal individuals are identified. Polyacrylamide gels of urines from bladder cancer, bladder papilloma, and normal individual exhibit clear differences in banding patterns. Urine from bladder cancer patients shows gels with increased quantities of low (less than 100,000) and increased and additional high (less than 100,000) molecular weight proteins when compared to gels with urine from papilloma and normal individuals. In order to localize and identify proteins in the urine from bladder cancer, papilloma, and normal individuals, proteins were separately fractionated on Sephadex G-200 columns and each elution fraction was reacted on Ouchterlony gel diffusion against various specific antisera. The qualitative analysis of proteins in urine from bladder cancer patients is discussed in relation to their molecular weight distribution in the Sephadex G-200 profiles and their possible role in tumor host relationships.