Cutaneous and subcutaneous blood flow (CBF, SBF) were studied in non-lesional psoriatic skin (NLS) of 10 patients with only minimal psoriatic skin manifestations, using the local 133Xe washout method. Measurements of the CBF and SBF in the NLS of the patients and 10 normal individuals yielded no statistically significant differences. The results of the present study indicate that the activity of psoriasis can be monitored by the CBF measurements in the NLS, since previously published values for CBF of NLS have shown increasing values with increasing psoriatic activity. The significance of these findings may be more evidence of humoral factors playing a role in the pathogenesis of the disease. The tissue-to-blood partition coefficient for 133Xe was calculated on the basis of biochemical estimations of the relative content of lipids, proteins, and water in skin biopsies from non-lesional skin sites of 8 psoriatic patients. The relative content of lipids, proteins, and water was normal. Thus, the normal 133Xe partition coefficient of 0.7 ml/g should be used for measurements of the CBF in NLS.