When pre-implantation embryos were transferred to the oviducts of pseudopregnant recipient females, on the 1st day post coitum, the percentage of females becoming pregnant was greater when a very small inoculum volume was used. The number of eggs injected per oviduct, in the range from two to ten, did not significantly affect the percentage developing into foetuses. The pregnancy rate was lower for one-cell than for two-cell and eight-cell eggs, morulae and blastocysts, but the percentage of eggs developing into live foetuses in those females which became pregnant was similar for all stages.