The concentration of plasma progesterone, oestradiol-17 beta, oestrone sulphate, corticosteroids and 13,14-dihydro-15-ketoprostaglandin F2 alpha (PGFM) was measured in 12 buffalo cows during the whole period of gestation, around parturition and for 15 d postpartum. The concentration of progesterone and oestradiol-17 beta increased slightly during the first 2 months (3.5 +/- ng/ml) and 4 months (14.8 +/- 2.1 pg/ml) of pregnancy, respectively. Their values remained consistently below these levels until near the end of the pregnancy period when progesterone concentrations decreased significantly (P < 0.05) at d 7 prepartum (0.9 +/- 0.1 ng/ml) and oestradiol-17 beta increased markedly (P < 0.01) at d 10 prepartum (26.3 +/- 2.6 pg/ml). Progesterone showed basal values (< 0.5 ng/ml) from d 4 prepartum to d 15 postpartum. Oestradiol-17 beta concentrations were maximal (82.8 +/- 3.6 pg/ml) during labour and returned to their basal values (< 12 pg/ml) at d 5 postpartum. The concentrations of oestrone sulphate remained low (< 140 pg/ml) during the first half of gestation period. It increased sharply (P < 0.01) thereafter to 5,620 +/- 116.5 pg/ml by 30 d prepartum and afterwards declined to about 50% of this value before calving reaching basal level (< 80 pg/ml) at d 2 postpartum. The concentration of corticosteroids fluctuated narrowly (1.7 +/- 0.3 ng/ml) throughout gestation, increasing significantly (P < 0.05) at d 12 prepartum (5.3 +/- 1.8 ng/ml) and peaking to 16.8 +/- 3.2 ng/ml at the moment of delivery. Its value declined below 3 ng/ml from d 3 onwards postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)