Plasma tryptophan and other putative amino acids, cortisol, folate and vitamin B12 and urinary biopterin (B) and neopterins (N) were measured in three groups of women: 62 women in the early postpartum period, 23 pregnant 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. Postpartum women had significantly lower tryptophan, vitamin B12 and significantly greater levels of cortisol, folate, neopterins and biopterins than controls. Comparisons between women who were classified on the EPDS as cases and non-cases revealed only a statistically significant difference for lower N:B (P<0.01) and lower folate (P<0.01) ratio in cases than non-cases. Multiple regression analysis showed a significant contribution for low tryptophan to increased EPDS which also showed significant correlations with low methionine, low tyrosine, low N:B ratio and high vitamin B12.