Hypofolatemia can cause psychiatric disturbances of a depressive nature. Pregnancy and delivery are often associated with hypofolatemia. This study was conducted to determine if hypofolatemia at day 3 post partum is a risk factor for baby blues or post partum depression. To study this hypothesis, 131 post partum women were followed prospectively for the 3 months immediately following delivery. 19% were found to have 'baby blues', as defined by a score greater than 20 on Pitt's scale (Pitt, 1968, J. Psychiatry 114, 1325-1335) and 12% had post partum depression as defined by a score greater than 7 on QD2A scale (Pichot et al., 1984, Rev. Psycholog. App. 34, 229-250, 323-340), within the three months post partum. No relationship was observed between the serum or erythrocyte folate levels on the third day following delivery and the maternal post partum depression scores. A statistically significant correlation between post partum depression and previous psychiatric disturbance was, however, observed.