A prospective study of 18 critically ill patients with community-acquired lobar pneumonia was undertaken at Hillbrow Hospital, Johannesburg, in order to document the initial plasma hormonal and substrate profile as part of the stress response to the infection. The results of these studies, carried out before therapy, were compared with the results in a group of healthy fasting adults. Highly significant (P less than or equal to 0.005) increases in the mean plasma levels of adrenaline, noradrenaline, human growth hormone, cortisol, glucose and free fatty acids were noted in the study group, with a lesser increase in the prolactin concentration (P less than or equal to 0.01). The levels of dopamine, glucagon, insulin and adrenocorticotrophin did not show any significant change. No significant differences were found in the hormonal profile when comparing survivors with non-survivors. The neuro-endocrine hormonal and metabolic responses in pneumonia appear to be similar to those seen in other stress situations and failure of the initial stress response does not appear to contribute to the mortality of critically ill patients with community-acquired lobar pneumonia.