The everted-sac technique was used to study the time-dependent effect of low Ca diet on Ca active transport along rat small intestine. In animals maintained on standard diet, active translocation of Ca was limited to proximal 10 cm of the intestine. In response to CA restriction, Ca transport in the duodenum was highly stimulated after 3 days, then gradually declined and after 28 days almost disappeared. In the proximal jejunum it was the highest between 7 and 21 days. In the distal ileum, the transport appeared after 3 days and increased progressively until 21 days, but markedly decreased at the 28th day. The normal pattern of Ca transport was reestablished on refeeding the animals with a standard diet.