Hofbauer cells are a major cell type of the human placental villous core particularly numerous at the beginning of pregnancy. In the present study we have investigated whether or not Hofbauer cells could subserve the function of accessory cells for colony formation by phytohemagglutinin stimulated allogeneic T cells. Results showed that Hofbauer cells are capable to play an accessory role on T cell proliferation probably due to the release of interleukin 1-like soluble factors.