In this paper we examine the relationship of serum levels of Ca, P, Ca X P, P/Mg, Ca X P/Mg, alkaline phosphatase, and iPTH to the development or regression of peripheral arterial calcifications (AC) in 44 patients with end-stage renal disease being treated by continuous ambulatory peritoneal dialysis (CAPD). The average follow-up time of this longitudinal study was 27 months (range 6-67 months). The patients were divided into two groups: Group A, those showing one or more increases of AC; and Group B, patients in whom AC either did not develop or decreased during the follow-up. There was no significant difference in serum Ca, P, Ca X P, alkaline phosphatase of iPTH between the two groups. However, serum Mg was significantly lower in Group A than in Group B (2.69 +/- 0.52 and 3.02 +/- 0.51 mg/dl, respectively, P less than 0.001), while the ratios P/Mg and Ca X P/Mg were significantly higher. Our observations suggest that in end-stage renal disease hypermagnesemia may retard the development of arterial calcifications.