Nifedipine was administered to 49 pregnant women with gestational hypertension as first-line therapy, and were longitudinally studied as paired observations for 3 or 10 day intervals of treatment with nifedipine until delivery. All the patients assumed a slow release formulation of nifedipine at the dose of 40-80 mg/24 hr in 2-3 administrations. Blood pressure was taken at least 4 times a day. The patients were divided in two groups: 32 women with non proteinuric gestational hypertension (NPGH) and 17 women with proteinuric preeclampsia (PP). No statistically significant modification of blood pressure was observed in both groups under treatment. However, NPGH showed a trend to reducing, while PP demonstrated a tendency to worsening both systolic and diastolic blood pressures. After treatment with nifedipine the platelet count of both groups was found unchanged. No adverse fetal or newborn effects imputable to the drug were observed. The present study demonstrates that nifedipine alone, at the doses used, is not effective in reducing blood pressure in long-term treatment. However the treatment could concur to avoid sharp and dangerous increases of blood pressure.