Immunoreactive levels of vasopressin (VP) and oxytocin (OT) were quantitated in the rat pineal gland in the middle of August, when nonapeptide levels have been reported to peak annually. The pineal levels of both VP and OT were found to be substantially elevated when sampled in August, compared to sampling in July and September. mRNA levels for OT and VP in hypothalamic nuclei (supraoptic, paraventricular, and suprachiasmatic nuclei) showed no such increases during August. A lesioning of the paraventricular nuclei did not suppress pineal VP and OT levels. Finally, the injection of colchicine into the third ventricle caused pineal VP and OT levels to increase substantially. Together, these results affirm the occurence of a summertime rise in pineal VP and OT levels and suggest that such increases do not derive from sites of VP and OT cell bodies in the hypothalamus. Rather, they indicate that the source of these pineal nonapeptides may be the pineal itself.