Abstract: The interaction of promastigotes of Leishmania with mouse peritoneal macrophage in vitro was studied by scanning electron microscopy. The results showed that when promastigotes had been incubated with 1/1 000 McAb for 1 h, morphological changes could be seen in most promastigotes, some promastigotes were lysed and some promastigotes although adhered to the macrophage, but no penetration could be seen. When 1/1 000 McAb had been inactivated at 56℃ for 1 h and then incubated with promastigotes, scanning electron microscopic examination showed the promastigotes closely adhered to the surface of macrophage with their anterior end "buried" within macrophage.The results of the present study suggested that the mechanism of promastigote-macrophage adhesion was ligand-receptor binding interaction (Figs. 1-11).