The influence of luminal lactose and glucose on intestinal calcium transport was examined in vivo in normal post-weaned young rats. In situ segments of duodenum, midgut and ileum were perfused through the lumen for 1 h with an isotonic solution of 3.4 mM calcium containing radioactive isotopic 45Ca as tracer and additionally either 10 mM lactose or 10 mM glucose or, for the control group, no saccharide. Net absorption was measured by disappearance of luminal calcium; lumen-to-plasma flux was determined from the disappearance of tracer 45Ca. This concentration of luminal lactose or glucose had no direct effect on calcium transport under these steady state conditions.