The purpose of this study was to determine the differences in endocrine responses, blood loss and arterial blood gas profiles between patients subjected to hypotensive anaesthesia or normotensive anaesthesia and those between patients given sodium nitroprusside (SNP) or nitroglycerin (NTG) as the hypotensive agent. 36 patients, who were scheduled to undergo mandibular osteotomy, were recruited for the study. Their hormonal responses, metabolic responses, arterial blood gas profiles and blood loss were determined during hypotensive anaesthesia induced by either SNP or NTG and normotensive anaesthesia induced by sevoflurane (SEV). Blood loss was smaller and the duration of surgery was shorter in the SNP and NTG groups than in the SEV group. The plasma levels of adrenocorticotrophic hormone, cortisol, vasopressin, norepinephrine and dopamine increased during surgery in all 3 groups. There were no significant differences in the hormone levels, among the 3 groups, or between the SNP and NTG groups.