The functional model of Cr kinetics and metabolism described by Lim et al. [Am J Physiol 1983;224:R445-R454] for healthy people was adapted to the specific situation of the continuous ambulatory peritoneal dialysis (CAPD) patient. For this purpose 3 CAPD patients were submitted to an acute <sup>51</sup>Cr-labelled dialysis dwell of 6 h. The rate of uptake of Cr in the plasma appeared to be equal to its disappearance rate from the peritoneal fluid. The plasma levels increased to a constant value in the first 2 h after the start of the dialysis session. The amount of Cr cumulatively excreted in the urine over the follow-up period of 10-12 days was 10-15 % of the amount absorbed during the acute dwell. The experimental pharmacokinetic data were in close agreement with the values predicted by the modified functional model for Cr(III) kinetics and metabolism. According to this model, the effect of long-term CAPD treatment (10 years) should result in an accumulation of Cr with a factor of 100 in those organs, especially liver and spleen, known to have a slow exchange of Cr with the central plasma compartment. This predicted and dramatic increase was in close agreement with the Cr concentrations found in liver tissue of 3 patients who died after a variable time on CAPD.