- The effects of blinding with or without pineal ablation on brain monoamine levels were studied in male rats. Brain dopamine (DA), norepinephrine (NE), epinephrine (E), and serotonin (5-HT) were measured by radioenzymatic assays. Four weeks following pinealectomy, E levels were significantly enhanced in the frontal cortex. Chronic blinding decreased striatal DA levels and increased striatal 5-HT levels in both sham-operated and pinealectomized (Px) animals. In a second experiment Px animals were sacrificed 1 or 7 d after pinealectomy in order to examine the short-term effects of pinealectomy. There were no differences between controls and Px animals in their cortical levels of DA, NE, and E and their hippocampal and hypothalamic 5-HT levels. However, the E concentrations measured 1 d after surgery were significantly greater than after 7 d. The implications of these findings with regard to the reported role of the pineal and melatonin in brain homeostasis and endocrine regulation are discussed.