Red blood cell (RBC) and polymorphonuclear white blood cell (WBC) calmodulin levels were measured in 25 uremic patients on regular hemodialysis. Uremic patients had significantly higher RBC [11.45 ± 0.66 (± SE) fg/cell] and WBC (590.5 ±110 fg/cell) calmodulin levels than normal subjects (8.62 ± 0.37 and 130 ± 30 fg/cell; P < 0.05). An extremely high RBC calmodulin level (20.58 fg/cell)was found in a patient with sickle cell anemia. Uremic patients on dialysis for 2 yr or more had lower RBC (10.99 ± 0.58 fg/cell) and WBC (390 ± 50 fg/ cell) calmodulin levels than those who were on dialysis for less than 2 yr (RBC, 12.30 ± 1.56 fg/cell; WBC, 943 ± 256 fg/cell; P < 0.05). There were no statistically significant differences in calmodulin levels when different subgroups of uremic patients were compared, e.g. patients with diabetes mellitus or those receiving supplemental vitamin D, anabolic steroids, or antihypertensive medications. We conclude that calmodulin levels are elevated in uremic patients on regular hemodialysis.