Rat hepatocytes and bone marrow stromal cells (BMSCs) were cocultured with the aim of maintaining differentiated hepatocyte functions. After BMSCs were expanded to a confluent monolayer, freshly isolated hepatocytes were cultured with them, separated by a semipermeable membrane. The BMSCs significantly increased the urea synthesis and albumin secretion activities of the hepatocytes. Conditioned medium prepared from a BMSC monoculture had the same effect. Further study showed that interleukin-6 was involved in the maintenance of urea synthesis and another factor in the maintenance of albumin secretion.