The effect of EEG-driven photic stimulation on stress-related endocrine function was studied. Subjects were 16 healthy males divided into a photic stimulation group (n = 8) and a control group (n = 8). Electrodermal and emotional lability measures were assessed by nonspecific skin conductance response and the Maudsley Personality Inventory, respectively. Plasma cortisol and beta-endorphin concentrations were measured both before and after EEG-driven photic stimulation as well as the resting condition. Subjects with electrodermal, emotional, or both lability showed comparable decreases of plasma beta-endorphin on photic stimulation as did the stable subjects. Under resting control conditions, however, they showed significant increases of beta-endorphin compared to both stable subjects as well as the photic stimulation condition. In addition, labile subjects showed significant alpha enhancement on photic stimulation compared to stable subjects and to the resting control condition. The data suggest that increases of plasma beta-endorphin in labile control subjects may denote a stress response to the conditions of these experiments, and that any decrease by EEG-driven photic stimulation may indicate a reduction of responsiveness to an acute stress.