The early diagnosis of bladder cancer is central to the effective treatment of the disease. Presently, there are no methods available to easily and specifically identify the presence of bladder cancer cells. The prevailing method for the detection of bladder cancer is the identification of bladder cancer cells by morphological examination of exfoliated cells or biopsy material by a pathologist. A hallmark of the malignant or transformed phenotype is an abnormal nuclear shape, the presence of multiple nucleoli, and altered patterns of chromatin organization. Nuclear structural alterations are so prevalent in cancer cells that they are commonly used as markers of transformation for many types of cancer. Nuclear shape is determined by the nuclear matrix, the dynamic skeleton of the nucleus. The nuclear matrix is the structural component of the nucleus that determines nuclear morphology, organizes the DNA in a three-dimensional fashion that is tissue specific, and has a central role in the regulation of a number of nuclear processes, including the regulation of DNA replication and gene expression. Previous investigations into prostate and breast cancer have revealed that nuclear matrix protein (NMP) composition undergoes alterations with transformation and that the nuclear matrix can serve as a marker for the malignant phenotype. In this study, we have identified NMPs with which it is possible to differentiate human bladder tumors from normal bladder epithelial cells. We examined the NMP composition of 17 matched tumor and normal samples from patients undergoing surgery for bladder cancer. We have identified six proteins present in all tumor samples that are not present in the corresponding normal samples and three proteins that are unique to the normal bladder tissues in comparison with the tumor samples. Five of the six bladder cancer-associated proteins were also identified in three human bladder cancer cells lines examined (253j, UMUC-2, and T24). Therefore, we have demonstrated that nuclear matrix composition is able to differentiate bladder cancer from normal bladder tissue and may provide useful tools for early detection and recurrence of the disease. Importantly, these markers may provide valuable tools for cytopathological screening for bladder carcinoma.