BACKGROUND: Early in vitro studies of blastocyst formation in several primate species have demonstrated the feasibility of such studies. Initial studies of in vitro-fertilized oocytes cultured with buffalo rat liver cells suggested that other epithelial cells might be used to assess blastocyst adherence and penetration in vitro. METHODS: Macaque blastocysts were incubated with different epithelial cell lines or with Matrigel. The interaction was studied using light and transmission electron microscopy. RESULTS: In general, zona-free blastocysts attached 2 days after placing on the substrates. MDCK cells provided optimal conditions for blastocyst development. The best preparations showed some development of an amniotic cavity and distribution of cytotrophoblast and syncytial trophoblast. Distribution of syncytial trophoblast at the margin of the site and cytotrophoblast centrally was similar to that seen at the trophoblastic plate stage in this species. However, there was less syncytial trophoblast than is normally found at this stage, and total time from fertilization to the trophoblastic plate stage was delayed 2 days. CONCLUSIONS: While in vitro studies with blastocysts cannot completely mimic the intrauterine environment, they can illustrate some of the potential interactions and provide a situation in which parameters may be manipulated.