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Ten minutes of exposure to increasing concentrations of sucrose caused a proportional decrease in the volume of sheep late morulae, their relative volume changed as a linear function of the reciprocal of the osmolality of the medium. Day 6 sheep and Day 7 cattle embryos responded to the addition of permeating cryoprotectants by an initial shrinkage which was followed by gradual reexpansion. After 1.25 min exposure the relative volumes of sheep and cattle embryos respectively were 20 and 25% smaller in glycerol than in ethylene glycol. The volumes of cattle and sheep embryos remained smaller in glycerol than in ethylene glycol up to the final observation at 30 min. The osmotic response of sheep late morulae to 2.0 M propylene glycol was intermediate between their response to 2.0 M glycerol and to 2.0 M ethylene glycol. These results indicate that Day 6 sheep and Day 7 cattle embryos are more permeable to ethylene glycol than to glycerol.