This study compared the levels of 18 red cell elements and 22 hair elements in 46 patients (median age: 36.2 yr) diagnosed with PMS (premenstrual syndrome) to 50 normals (median age: 37.7 yr). Significantly lower amounts of calcium, chromium, copper, and manganese were found in the blood of patients with PMS. The ratios of Mg/Ca and K/Na and toxic metals such as lead, arsenic, and germanium were significantly elevated in the PMS patients. In hair, mercury and the Zn/Cu ratio were significantly greater in the PMS patients than the controls, but iron, potassium, and the Mg/Ca ratio were lower. The highly significant Mg/Ca ratio in blood cells may be indicative of a more complex relationship between PMS and magnesium and calcium than either element alone. The significantly lower blood cell calcium level found in these studies may provide additional evidence that PMS may be related to a calcium-deficiency state or a metabolic defect involving calcium.