Aluminum (Al) is recognized as a toxin in patients with deficient renal function. Moreover, Al may play a role in some neurodegenerative diseases. It is hypothesized that more than one intestinal absorption mechanism exists for Al, related to various intraluminal chemical species, and that Al shares intestinal transport routes for essential inorganic substances due to similarities in their chemical speciation characteristics. The purpose of the present investigation was to study the effects of ionic Na (0-120 mmol/l) and Ca (0-10 mmol/l), alone and in combination, on the intestinal absorption of ionic Al (20 and 30 mmol/l). A previously standardized method of perfusion of rat small intestine was used, combined with serial blood sampling. Mucosal uptake and systemic appearance of Al in the blood were monitored during 1 h perfusion, together with Na and Ca; the metals were given as the chloride. The intestinal absorption of Na and Ca was taking place according to previously reported mechanisms. A one-sided negative interaction was shown to exist between Ca and Al resp. Al and Na during both mucosal uptake and systemic appearance; Ca interacts negatively with Na during systemic appearance, but enhances mucosal uptake of Na. It may be speculated that Al mimicks Ca in its Na-dependent intestinal passage.