In this study, we tried to replicate the finding of a diminished cortisol response to stress in autistic-like patients in a more homogenous Multiple Complex Developmental Disorder (MCDD) group. MCDD forms a distinct group within the autistic-like disorders, characterized by impaired regulation of anxiety and affective state, impaired social behavior/sensitivity, and thought disorder. A number of MCDD children develop schizophrenia in adult life.Responses to a psychosocial stressor, consisting of speaking in public while recorded on video, were measured in 10 MCDD children and 12 healthy control children. The public speaking test was imbedded in a two-hour test session, and compared to a control test session. Hypothalamic-pituitary-adrenal (HPA) responses were measured on salivary cortisol at about 20-minute intervals. Heart rate was measured continuously. Delta AUC's were computed for both heart rate (dAUCHR) and salivary cortisol (dAUCCORT), as a measure of response to the test.The public speaking task resulted in significant responses in heart rate and salivary cortisol in healthy control children, but not in MCDD children. dAUCHR was 3.28±2.37 in healthy control children, but -0.09±1.73 in MCDD children (t=3.31, P<0.01). dAUCCORT was 3.22±3.16 in healthy control children, but 0.17±1.74 in MCDD children (t=2.72, P<0.05).The impaired responses to psychosocial stress found in MCDD children may be the result of their limited abilities to react adequately to their (social) environment. The same impairment in stress processing has been found in schizophrenia, and might be a factor in the vulnerability of these MCDD children to develop schizophrenia. (C) 2000 Elsevier Science Ltd.