The successful in vitro culture of sheep and cattle ova is reported. Fertilized sheep and cattle ova have not been reported to develop readily in vitro. However, this study describes the successful culture of sheep ova from one-cell to eight-cell stages to the morula and blastocyst stages, and cattle ova from one-cell and eight-cell stages to the morula and blastocyst stages. The study also reports high embryo survival after transfer to recipient animals. Welsh mountain ewes were superovulated and mated. Embryos were flushed from the reproductive tract in a modified Dulbecco's phosphate-buffered salt solution (PBS) supplemented with various components. The ova were cultured in a synthetic oviduct fluid (SOF) medium, which was based on the biochemical analysis of sheep oviduct fluid. The medium contained various salts, sugars, and proteins, and had an osmolarity of 270 mosmol and a pH of 7.2 to 7.4. The study examined the development of sheep ova in various oxygen concentrations. The results showed that ova cultured in 5% oxygen developed most readily in vitro. Ova cultured in higher oxygen concentrations were less developed. The study also examined the development of cattle ova in SOF. The results showed that cattle ova cultured in SOF developed at a similar rate to in vivo development. The study found that the combination of a satisfactory medium and gas phase allowed sheep and cattle ova to be cultured from the early cleavage stages to viable morulae and blastocysts. The study also found that the sheep ovum could develop through the supposed 'block to development'. The results show that the successful culture of sheep and cattle ova is possible with the right medium and gas conditions.The successful in vitro culture of sheep and cattle ova is reported. Fertilized sheep and cattle ova have not been reported to develop readily in vitro. However, this study describes the successful culture of sheep ova from one-cell to eight-cell stages to the morula and blastocyst stages, and cattle ova from one-cell and eight-cell stages to the morula and blastocyst stages. The study also reports high embryo survival after transfer to recipient animals. Welsh mountain ewes were superovulated and mated. Embryos were flushed from the reproductive tract in a modified Dulbecco's phosphate-buffered salt solution (PBS) supplemented with various components. The ova were cultured in a synthetic oviduct fluid (SOF) medium, which was based on the biochemical analysis of sheep oviduct fluid. The medium contained various salts, sugars, and proteins, and had an osmolarity of 270 mosmol and a pH of 7.2 to 7.4. The study examined the development of sheep ova in various oxygen concentrations. The results showed that ova cultured in 5% oxygen developed most readily in vitro. Ova cultured in higher oxygen concentrations were less developed. The study also examined the development of cattle ova in SOF. The results showed that cattle ova cultured in SOF developed at a similar rate to in vivo development. The study found that the combination of a satisfactory medium and gas phase allowed sheep and cattle ova to be cultured from the early cleavage stages to viable morulae and blastocysts. The study also found that the sheep ovum could develop through the supposed 'block to development'. The results show that the successful culture of sheep and cattle ova is possible with the right medium and gas conditions.