Previous observations have suggested a role for the pineal gland in regulation of blood pressure. To investigate this possibility, pinealectomy was performed in prepubertal (43-day-old) and postpubertal (55-day-old) male rats. Systolic blood pressure (BP) was measured by the tail cuff method in conscious pinealectomized (Px) and sham pinealectomized (ShPx) rats at various times. In the 3 weeks following surgery, the BP increase after Px was twice that after ShPx (p less than 0.05). During administration of 1% saline as the sole fluid source from day 96-123, hypertension (BP greater than 150 mmHg) was observed in those animals Px at day 43 (p less than 0.05 vs ShPx) but not in those Px on day 55. Moreover, saline consumption was increased in the hypertensive group compared to ShPx controls. There was no significant difference in mean body weight or heart rate between Px or ShPx groups. These data suggest that pinealectomy in the prepubertal period may result in a tendency to hypertension, measurable in conscious rats, which is unmasked by saline administration.