Birth complications such as perinatal asphyxia are considered risk factors for later neurobehavioural disorders. Behavioural analysis of animal models may help to clarify the contribution of particular patterns of early hypoxia and their combination to psychiatric morbidity. Wistar rats underwent caesarean section (c-section) alone or c-section followed by asphyxia, the latter induced by placing pups still in uterus horns into a water bath at 37 degrees C for 20 min. Vaginally delivered pups were used as controls. Frequency of ultrasound emissions was analysed following isolation at a lower temperature than that of the home nest (23+/-0.5 degrees C) and reunion with their mother (3 min) on postnatal day (PND) 13 (maternal potentiation test). A sex-dependent effect of hypoxia was observed, with higher production of ultrasounds in hypoxic males. Caesarean-delivered pups produced significantly more ultrasounds than those vaginally delivered. At adolescence (PND 35) rats underwent a 25 min social interaction test with a conspecific of the same sex and age. Significant alterations in investigative behaviour (inclusive of: nose, anogenital, body sniffing, and following) were evident in caesarean-delivered rats of both sexes, but not in rats experiencing perinatal asphyxia. At adulthood, auditory, and context conditioned responses, analysed in a fear conditioning test, were not markedly affected either by c-section or c-section plus hypoxia. However, hypoxic rats emitted significantly more 22 kHz ultrasounds than c-section or vaginally delivered rats during the training session. In conclusion, differential effects appear to be brought about by c-section and by hypoxia mainly related to emotional/anxious responses.