An open compartmental model for describing aluminium biokinetics is presented with a central compartment consisting of transferrin- and citrate-bound aluminium in blood plasma and interstitial fluid, and three peripheral compartments for organs, muscles and bones and the gastro-intestinal tract. The rate constants describing the transport of aluminium are normalized to an estimated plasma volume and do not depend on the size of the individual. Effects due to changes in compartmental sizes or to transport characteristics are described. The model is applied to biokinetics studies of a volunteer after i.v. administration and of Sprague-Dawley rats with different iron status and with nephrectomization after p.o. administration of 26Al.