Single graded doses of 1,25-dihydroxycholecalciferol of 2 and 4 μg were added intraperitoneally into the overnight 1.5% glucose dialysate of 6 patients on continuous ambulatory peritoneal dialysis. The effect on peritoneal macrophage chemotaxis and random migration was studied and compared with the baseline when no 1,25-(OH)₂D₃ was added. No consistent effect on peritoneal macrophage chemotaxis was observed. Random migration was significantly depressed at 4 μg when compared with baseline (5.4 ± 1.9 vs. 12.2 ± 3.7 cells/high-power field, p < 0.05). The potential clinical role of 1,25-(OH)₂D₃ as an immune modulator requires further study.