Plasma cortisol, prolactin, oestrogen, progesterone, thyroxine, thyrotrophin (TSH) were collected from 23 pregnant, 70 postpartum women at 7 days postpartum, and 38 non-gravid controls. Sixty two postpartum women were screened for depression by the Edinburgh Postnatal Depression Scale (EPDS) on day 7 after delivery and 34 of them were assessed by the Present State Examination (PSE) at 8 +/- 2 weeks after delivery. Postpartum women had a significantly greater level of cortisol, prolactin, thyroxine and oestrogen than non-puerperal women. Postpartum women with current depression (EPDS > or = 11) had significantly lower plasma prolactin levels than those without depression and those who developed depression within 6-10 weeks after delivery (PSE level > or = 5) had significantly lower plasma prolactin and significantly greater progesterone levels than those who were not depressed. There were significant correlations between age and plasma cortisol and prolactin levels. Higher thyroxine levels predicted greater severity of concurrent symptoms of depression (total EPDS score) whilst higher progesterone and lower prolactin levels predicted the occurrence of depression (total PSE score) 6-10 weeks after delivery. Women who breastfed had significantly lower EPDS and total PSE scores and higher plasma prolactin levels than those who did not breastfed their infants whilst women who had previous episodes of depression had significantly greater EPDS and PSE scores, lower prolactin and higher TSH levels than those who had not suffered from previous episodes of depression.