Single graded doses of 1,25-dihydroxycholecalciferol of 2 and 4 micrograms 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 micrograms when compared with baseline (5.4 +/- 1.9 vs. 12.2 +/- 3.7 cells/high-power field, p less than 0.05). The potential clinical role of 1,25-(OH)2D3 as an immune modulator requires further study.