Magnesium (Mg) is effective in the treatment of pregnancy-induced hypertension (PIH). In order to determine if patients with PIH are Mg deficient, we assessed mononuclear cell magnesium content (mMg) and serum Mg concentrations (sMg) in 23 normal pregnant women and in 12 women with PIH admitted in active labor. The sMg concentration in women with PIH was 1.74 +/- 0.1 mg/dl (mean +/- SD) and was not significantly different from normal pregnant women at 1.69 +/- 0.2 mg/dl. Both groups had sMg concentrations lower than in normal, non-pregnant controls (sMg = 1.96 +/- 0.1 mg/dl, p less than 0.001). The mMg content in normal pregnant women did not differ significantly from that in women with PIH (1.54 +/- 0.26 micrograms Mg/mg protein and 1.50 +/- 0.26 micrograms Mg/mg protein respectively). The normal control mean mMg was 1.36 +/- 0.17 micrograms Mg/mg protein, slightly lower than in normal pregnancy (p less than 0.005) and PIH (p less than 0.02). Mononuclear Mg content did not correlate with sMg concentration. These data suggest that PIH is not associated with an intracellular Mg deficit. Further studies utilizing other measures of intracellular Mg are indicated to assess the presence or absence of Mg deficiency in patients with both normal pregnancy and pregnancy complicated by PIH.