Se-aluminum was measured in a study group and a control group of undialyzed chronic uremic patients having a similar reduction of kidney function (median GFR 7 [range 5-15] ml/min/1.73 m2). Se-aluminum values (0-11, median 3, micrograms/l) in the control group (31 patients) receiving no treatment with aluminum-containing phosphate-binding gels, were all below the upper normal range (17 micrograms/l). The study group (28 patients) was treated with oral Al(OH)3 for 0.5-18 (median 6) months. Se-aluminum in this group was 17-230 (median 35) micrograms/l. It is concluded that se-aluminum increases in undialyzed chronic uremic patients ingesting aluminum-containing antacids. The study suggests that se-aluminum varies with the daily dose of aluminum hydroxide, and that se-aluminum in particular increases when the daily doses are more than 3 g Al(OH)3.