Abstract Introduction The aim of the present study was to investigate the effects of the stress response on plasma insulin, cortisol, glucose, and urinary vanilmandelic acid during weaning and after extubation, using pressure support (PS), continuous positive airway pressure (CPAP) and T-piece modes. Methods Sixty patients were randomly divided into three groups (n = 20). The PS group received FiO2 ≤ 0.4, PS ≤ 10 cmH2O, and positive end expiratory pressure ≤ 5 cmH2O for 2 hours. The CPAP group was given FiO2 ≤ 0.4 and CPAP 5 ≤ cmH2O for 2 hours. The T-piece group (group T) received 4 l/min oxygen via a T-piece for 2 hours. After 1 hour and 2 hours in their respective weaning modes, blood and urine samples were taken for insulin, cortisol, glucose and vanilmandelic acid measurements. Forty-eight hours after extubation, blood and urine samples were again taken. Results Plasma insulin was greater in group T than in the PS and CPAP groups (P < 0.01 and P < 0.01). The plasma cortisol concentration was greater in group T than in group PS during weaning (P < 0.05) and after extubation (P < 0.05). Blood glucose concentrations were greater in group T than in the other groups (both P < 0.01) both during weaning and post extubation. Urine vanilmandelic acid was greater in group T than in the other groups during weaning and after extubation (both P < 0.001). Conclusion Weaning via the T-piece caused a greater stress response than the PS and CPAP modes.