Biofeedback equipment is intended to train conscious regulation of normally sub-conscious processes like autonomic nervous system activities. The manufacturers claim that measurements made with the equipment are accurate enough for research purposes, but these claims have not been vigorously tested. The subconscious processes recorded with biofeedback equipment are often disturbed by stress, and the aim of this study was to determine if the markers of stress could be accurately determined with biofeedback equipment. The physiological processes that were screened were:<ul><li> Time and frequency domain heart rate variability (HRV) determined from blood-volume-pulse (BVP) </li><li> Time and frequency domain HRV determined from electrocardiogram (ECG) </li><li> The amplitude of the BVP</li><li> Electromyographic (EMG) activity</li><li> The pulse transit time</li><li> Respiration rate and depth</li><li> Skin conductivity</li><li> Fingertip temperature</li><li> Quantitative electroencephalographic (QEEG) activity</li></ul> The accuracy of the HRV measurements were tested by comparing them to readings made simultaneously with a gold-standard device (Actiheart), and the main findings were:<ul><li> The hardware capabilities of the two systems are comparable when it comes to registering heartbeats and calculating heart rate</li><li> The frequency domain biofeedback HRV variables had relatively good correlations to the Actiheart results, but improvements are necessary</li><li> Frequency domain HRV variables differ when calculated with fast Fourier transform or with autoregression</li><li> The BVP signal is prone to movement artifact and other forms of interference</li></ul> The HRV measurements of both the biofeedback and Actiheart device were correlated to psychometric evaluations of anxiety and burnout, two conditions closely related to the concept of stress. The main findings were:<ul><li> Worry and anxiety can have a cardiac accelerating effect, largely mediated by vagal withdrawal </li><li> A decrease in resting autonomic variability associated with anxiety</li><li> Significant autonomic nervous system inflexibility occurs in the face of a cognitive stressor with increased anxiety</li><li> An increase in vagal and a decrease in sympathetic cardiac control correlated with increased levels of vital exhaustion</li><li> HRV assessment with specialized software such as Polar Precision Performance Software and the advanced HRV Analysis 1.1 software for windows (Biomedical Signal Analysis Group) were superior to assessments by means of the Biograph Infinity program</li></ul> Next it was investigated whether any association existed between levels of anxiety, burnout and that of Biograph-derived physiological indicators such as BVP amplitude, BVP HRV, ECG HRV, pulse transit time, EMG, fingertip temperature, respiration rate and amplitude, skin conductivity and QEEG levels. The overriding observations with increases in the levels of stress-related emotional conditions such as anxiety were that of a decrease in variability in almost all physiological functions assessed by Biograph. In conclusion, relatively good associations were found between certain, but not all, Biofeedback monitor results and that of other assessments of stress. The potential exists to develop a program which would accurately reflect stress levels.