1. The pineal has been shown to have a role in controlling reproduction of polyestrus mammals (like humans and laboratory rodents). It influences the age of sexual maturation; the timing of the ovulatory cycle; and gonadal steroidogenesis. 2. Here the authors report the early and late effects of pinealectomy (Px) and sham-pinealectomy (SPx) on the estrous cycle periodicity, plasma LH, FSH and urinary 6-sulphatoxymelatonin (6-SMT) excretion in female rats. 3. Female Wistar rats (3-4 months of age) were maintained on 12/12 L/D cycle. Orbital venous plexus blood and urine samples were collected from the same rat during the estrus phase before surgery, 4-7 and 55-60 days post surgery. 4. Daily vaginal smears were taken to monitor the estrous cycle and they showed a time dependent increase in the estrus stage duration in Px rats (estrus stage: 1 day in control; 3-4 days after 45 days Px). 5. The decrease of gonadotropins at early post Px was due to surgical stress. 6. 6-SMT levels were significantly lower at 4-7 days post SPx, but at 55-60 d post surgery these levels returned to control values, which indicate pineal gland integrity. The reduction in urinary 6-SMT may be attributed to a possible high level of plasma corticosterone occurring after surgical manipulations. 7. 6-SMT levels in Px rats were extremely lower at 4-7 and 55-60 days post surgery, but not null, confirming the surgical removal of the pineal gland and indicating the synthesis of melatonin in sites other than the pineal gland.