Kainic acid (KA) is a powerful convulsant and neurotoxic agent. In the present paper the acute and long term effects of intrahippocampal KA administration on estrous cycle and on serum concentrations of progesterone were studied in adult female rats. Following KA injection, 3 distinct periods were observed: 1) acute period (24-48 h), 2) silent period (21-30 days), and 3) chronic period, characterized by the appearance of spontaneous recurrent seizures (30-45 days). KA administration did not affect progesterone levels during the acute period. In contrast, during the silent period, KA-treated animals exhibited irregular estrous cycling and decreased progesterone levels. These results are of interest in view of a possible link between epileptic phenomena and hormone secretion.