The diurnal variation of plasma oestrone (E1), oestradiol (E2), oestriol (E3), progesterone (P), cortisol (F) and dehydroepiandrosterone sulphate (DHAS) and saliva E1, E2, E3, P and F was investigated in matched plasma, and saliva samples were obtained hourly from 08.00 to 24.00 h and at 04.00, 07.00 and 08.00 h from nine pregnant women (3 at 30, 3 at 34 and 3 at 38 weeks gestation). A diurnal variation in plasma and saliva cortisol levels was found in all subjects and in plasma DHAS in 8 out of 9 subjects. No consistent diurnal variation was found at any gestation in any of the other hormones in plasma or saliva. There was a significant correlation between saliva E3 and P levels at 30 weeks gestation but no other consistent correlations between hormone levels were found at any gestation.