Bright white light therapy (two-week courses of daily morning sessions lasting 1 h; distance from lamp 60 cm; light intensity 3300 lux) was used in 51 patients with neurotic autonomic dystonia syndrome. Improvements were obtained in 59% of patients (group 1), while treatment was not effective in 41% (group 2). Changes in virtually all neuroendocrine, motivational, psychoautonomic, pain, and psychopathological symptomatology were obtained. At the end of treatment, patients in group 1 had increases in the EEG power spectrum, increases in slow activity and reductions in rapid activity on both sides; coefficients of asymmetry approached those in controls, and there were increases in urinary excretion of catecholamine and serotonin metabolites. In group 2, initially increased EEG power spectra increased further, because of increases in theta and beta rhythms bilaterally, and the coefficient of asymmetry decreased sharply; total excretory activity decreased. Symptoms and psychophysiological measures positively and negatively affected by phototherapy were identified.