The immune system is important in the pathogenesis of psoriasis and emotional stress has precipitated psoriasis in many patients. Neuropeptides, alpha-Melanocyte stimulating hormone (alpha-MSH), beta-endorphin, met-enkephalin and substance P (SP) act as immunomodulators, and their secretion increases during periods of stress. To see whether these neuropeptides themselves might be related to psoriasis and/or to the aggressiveness of the disease, we evaluated the plasma neuropeptide levels in 13 patients with active psoriasis (patients with new lesions and/or pre-existing lesions that had become larger during the month before the study), in 11 patients with stable psoriasis and in 10 healthy controls. Plasma concentrations of neuropeptides were evaluated by RIA (immunoradiometric assay for beta-endorphin). Data were compared by the Student t-test for unpaired data. There were no significant differences between the plasma levels of any of the neuropeptides between active psoriatic patients and stable psoriatic patients, nor between the plasma levels of neuropeptides of psoriatic patients and those of control subjects. It seems unlikely that circulating neuropeptide levels are of primary importance in the manifestation of the psoriatic skin lesions.