Day 7 cow embryos were frozen in 1.5 M-DMSO [dimethylsulfoxide] in PBS [phosphate-buffered saline] at 0.3.degree. C/min to -36.degree. C and at 0.1.degree. C/min between -36 and -60.degree. C before being plunged directly into liquid N. They were subsequently thawed (rapidly to -50.degree. C, at 4.degree. C/min from -50 to -10.degree. C and rapidly again) to room temperature. Embryonic viability was tested by 4 different transfer techniques. Maximum pregnancy rate (8/12) was obtained with surgical transfer immediately after thawing and dilution of DMSO.