Twenty-four male, 6- to 8-week-old Sprague-Dawley rats were fed one of two skim-milk-based diets or stock laboratory diet for 100-120 days to assess the effect of dietary and infused lactose on intestinal lymph lipids. One skim-milk-based diet had its lactose enzymatically hydrolyzed by commercial beta-galactosidase to its constituent monosaccharides galactose and glucose, while the second skim milk diet was unaltered. Serum triglycerides, but not serum cholesterol, were higher in the lactose- versus the glucose-/galactose-adapted rats at 90 days. There was no diet-associated qualitative difference in serum lipoproteins as analyzed by agarose gel electrophoresis. After the rats had consumed the diets for 100-120 days, 0.9% saline and 20% solutions of lactose, and equimolar mixtures of glucose/galactose, glucose and maltose were infused sequentially via a duodenal cannula, then intestinal lymph was collected via a mesenteric lymph duct cannula, the only significant difference was a 134% increase in lymph cholesterol, but not lymph triglyceride output, when lactose was infused into lactose-adapted rats.