Pleiotrophin (PTN) and midkine (MK) form a distinct family of heparin binding growth factors. In a variety of human cancers, MK mRNA levels have been found to be increased as compared to adjacent non-cancerous tissues. We examined the expression of PTN, its putative receptor, namely protein tyrosine phosphatase zeta (PTPzeta, also known as RPTPbeta), and a related protein, receptor-type protein tyrosine phosphatase gamma (RPTPgamma), in human colorectal cancers and the adjacent normal mucosae. PTN and PTPzeta mRNA levels were generally decreased in colorectal cancers as compared to those in adjacent normal mucosae, while the RPTPzeta level was not significantly different between them.