This study evaluated the effect of the inclusion of skimmed milk in freezing extenders on the motility, viability and acrosome morphology of canine spermatozoa after thawing. The Tris-glucose-citric acid buffer of a semen extender, which also included 20% egg yolk, 5% glycerol and 0.25% SDS, was replaced with 0, 50 or 100% skimmed milk. After thawing, the proportion of motile spermatozoa was not significantly different among semen extenders during incubation for 120 min at 37 degrees C. At 120 min after thawing sperm viability was significantly greater when an extender in which the buffer had been completely replaced by milk was used than in an extender in which the buffer had been partially replaced (P < 0.05). Acrosome morphology after thawing was similar for the three extenders tested. A considerable decrease in sperm motility and viability was observed during incubation, which may be due to concentrations of SDS that were not optimal. From these results it was concluded that the use of skimmed milk in extenders for freezing dog semen results in sperm motility and viability after thawing comparable to that obtained using a Tris-based buffer.