Mental stress induces cardiovascular effects. The postural changes that arise during passive head up tilt (HUT) elicit complex cardiovascular and hormonal changes. We investigated the effects of posture on mental challenge by comapring mental challenge induced cardiovascular and salivary responses in supine and upright tilted participants. 18 healthy young males were subjected to two mental challenge, applied using mental arithmetic (MA), protocols: a) MA in supine position and b) MA during HUT (MA + HUT), with sessions randomized and >=2 weeks apart. Beat to beat continuous hemodynamic variables were measured and saliva samples taken for hormonal assay.In relation to baseline, MA in supine position increased HR (+8.0±6.0 bpm), MAP (+10.0±6.5 mmHg), CO (+0.6±0.8 l/min), TPR (+27±134dyne*s/cm⁵) but decreased SV (-2.0±7.9 ml). However, MA + HUT increased HR (+28.8±8.4 bpm, p< 0.001), MAP (+11.2±11.6 mmHg) and TPR (+160±199dyne*s/cm⁵) but SV (-34.5±14.6 ml, p< 0.001)) and CO (-0.2±1.0 l/min, p<0.01) decreased. Mental challenge affects the cardiovascular responses dependent on the posture. Physiological alterations observed in models combining mental stressors and changes in body posture, such as in public speaking, must be interpreted with caution. The physiological responses to these combined stressors are not entirely due to the effects of mental challenge per se but may be modulated by the posture assumed by the subjects during the tests.