The objective was to assess the relationship between vulnerability to postpartum depression and perceptual defense evoked by tachistoscopic stimuli alluding to perinatal themes in pregnant women. Tachistoscopic stimuli have been shown to produce different thresholds of conscious identification according to their emotional content: a phenomenon termed perceptual defense. A total of 412 women in their 3rd of 4th month of pregnancy were asked to identify 14 pictures and 18 verbal stimuli shown for initially very brief but increasing durations. Presentation times required for a correct identification were measured. Depression was assessed, at 2 and 6 months postdelivery, by the Hamilton Depression Rating Scale: 53 women were defined as depressed by a score > or = 15. Discriminant analysis showed that the women who would become depressed 7 to 11 months later were slower than the nondepressed to identify 5 stimuli alluding to pregnancy, sexuality or a father image. Particular attitudes towards the themes of being pregnant, of sexuality and of the father could be components of a psychological predisposition to the development of depressed mood in the postpartum.