The study was performed to compare the galactose tolerance of male and female pigs to 5% galactose and 25% hydrolysed whey (HW; containing 5% galactose) diets. Plasma galactose and dulcitol levels were measured throughout the diet period and correlated with the lens dulcitol contents at the end of the period. On the first day of the diet there was no significant difference between male and female blood galactose levels after galactose ingestion. The consumption of HW resulted in a significant 30% decrease in the blood galactose peak in females; there was no parallel difference in males on the HW diet. The 30-day diet induced a significant decrease in galactosaemia peaks resulting from galactose ingestion in both males and females, indicating an activation of galactose metabolism. The HW diet resulted in an equivalent decrease in peak galactosaemia only in males, cancelling the initial differences observed between males and females. The final dulcitol content in the lenses appeared to be correlated with plasma galactose but not with plasma dulcitol. However, the differences in plasma galactose between males and females, or between the two diets, resulted in smaller and often non-significant differences in lens dulcitol.