This experiment was designed to evaluate the ability of 4 different types of somatic cells to promote development of early cleavage in rat embryos. Embryos were collected from Wistar-Imamichi rats. Four and 8-cell rat embryos were co-cultured with rat granulosa, oviductal, uterine and kidney monolayer cells. The culture was performed in TCM 199 supplemented with 10% fetal calf serum, sodium lactate and pyruvate alone (m199FCS). Among the co-culture systems, morula and blastocyst development was better with granulosa, oviductal and uterine cells (98.6, 95.6 and 94.1%, respectively) than with m199FCS alone and kidney cells (77.6 and 73.7%, respectively). Similarly, 4-cell rat embryo development also followed the same trend and the development percentages with granulosa, oviductal, uterine, kidney cells and m199FCS alone were 32.0, 30.7, 29.3, 0 and 2.7%, respectively. Nevertheless, 8-cell embryos were developed to hatched blastocysts in co-culture with oviductal, uterine cells and in the conditioned medium of oviductal cells, 21.0, 19.0 and 2.1%, respectively. But co-culture with granulosa, oviductal and uterine cells represented the best physiologic approach and showed superiority to the other cell types. Forty-four of 184 1-cell embryos co-cultured with oviduct cells developed to the morula/blastocyst stage. The co-culture of early rat embryos in a medium with oviductal explants can support further development.