Relatively little is known about the individual steps in intestinal copper absorption and whether or how they may be regulated. PolarizedCaco2 cell monolayers with tight junctions offer an already tested model in which to study intestinal metal transport. This model was used to examine potential effects cellular copper availability. Uptake and transport were determined upon application of ⁶⁴Cu(II) to the brush border. In the range of 0.2-2µM, uptake was dose dependent and in the range of 20% of dose, per 90 min. Overall transport of ⁶⁴Cu across the basolateral surface was about 0.3%. When cellular copper levels were depleted 40%, by 18h pretreatment with the specific copper chelator triethylenetraamine, uptake and overall transport were markedly increased, going to 80 and 65% of dose, respectively. Cellular retention of ⁶⁴Cu fell 4-fold, from 6 to 1.5%. Depletion of copper with the chelator was rapid and preceded initial changes in uptake and overall transport by 4h. A lesser depletion of cellular copper (13%) failed to enhance copper uptake but doubled the rate of overall transport, as measured with ⁶⁴Cu and by atomic absorption. As previously reported, pre-exposure of the cells to excess copper (10µM, 18h) also enhanced copper uptake (about 3-fold). In contrast, ascorbate (10-1000µM) failed to significantly alter uptake and transport of 1µM ⁶⁴Cu. Our findings are consistent with the concepts that, in the low physiological range, copper availability alters the absorption capacity of the intestine to support whole body homeostasis, and that basolateral transport is more sensitively regulated than uptake.