To compare the antihypertensive efficacy of methyldopa administered once at bedtime with the same total dose given three times daily, a double-blind crossover study was performed in 14 patients previously well controlled on methyldopa. Each patient received a total daily dose of 0.375 gm, 0.75 gm, or 1.5 gm of methyldopa, depending on the dose of drug that had previously been successful in that individual. The trial design included either 12 wk of methyldopa three times daily (TID) followed by 12 wk of single daily bedtime (HS) doses of methyldopa or administration of drug in the reverse order. Supine and erect blood pressures were recorded 4 times daily (8 A.M., 12 noon, 4 P.M., and 8 P.M.) every 4 wk throughout the study. Blood pressure control was excellent in all patients whether the drug was administered three times daily or at bedtime. Systolic pressures were slightly lower at 8 A.M., when methyldopa was given at bedtime than on doses three times daily, and systolic and diastolic pressures were slightly higher at 8 P.M. that at 8 A.M. on the bedtime regimen.