The amount of pain experienced by the postoperative newborn remains one of the most challenging problems in neonatology. In this study, ethological methods were used to examine behaviours for 12 hours, commencing 24 hours postoperatively in three male full-term infants following chest surgery. The infants' facial expressions, body postures and movements were coded each minute from videotapes. The infants' heart rates and respiratory rates were also continuously recorded. Behavioural data were analysed using descriptive statistics and factor analysis. The six-factor solution accounted for 61.6% of the variance and identified indices of acute distress, subacute pain, quiet alertness, drowsiness and sleeping. Changes were evident when comparing behavioural or physiological variables before and after the administration of analgesia, treatments, nursing care or environmental noise. The authors conclude that ethological methods are appropriate to examine this problem, and recommend that the study be replicated.