Early development of bovine oocytes fertilized in vitro in the medium with caffeine and heparin was examined in different culture systems. When the oocytes were transferred into culture medium 8 h after insemination, 12%(7/60) of penetrated oocytes cleaved to 4-cell stage 24 h after insemination. The proportions of oocytes cleaved to 80to 16-cell stage 48 h after insemination had also a to be higher in oocytes transferred into culture medium 8 h (29%) than 16 h(10%) or 24 h(4%) after insemination. 52% of the 4-cell embryos developed to morula and blastocyst stages when they were co-cultured with oviductal epithelia, whereas only 5% of embryos cultured without the epithelial cells(P<0.001). In another experiment, embryos were co-cultured with ampulla, isthmus or utero-tubal junction of oviducts. There are no significant differences in the proportions of embryos developed to morula and blastocyst stage.