1 Phenylethanolamine-N-methyltransferase (PNMT) activity in adrenal gland was lower than the control values at day 24 of rabbit pregnancy and fell throughout the gestational period. 2 Catechol-O-methyltransferase (COMT) activity during pregnancy and parturition followed a similar pattern to PNMT. 3 Adrenaline content of the adrenal gland declined significantly during the last few days of pregnancy but at parturition showed a tendency to return towards normal. 4 The biochemical mechanisms which result in a decline in PNMT and COMT activities and adrenaline concentration appear to be the consequence of modifications in endocrine gland secretion during pregnancy.