The authors have tested the hypothesis that the deficiency of bile acids and the consequent endotoxin translocation might play a role in the pathogenesis of psoriasis. Under normal conditions the bile acids act as detergents (physico-chemical defense) and can protect the body against enteric endotoxins by splitting them into nontoxic fragments and thus preventing the consequent release of cytokines [Persp. Biol. Med. 21 (1977) 70]. A total of 800 psoriasis patients participated in the study and 551 were treated with oral bile acid (dehydrocholic acid) supplementation for 1-8 weeks. The efficacy of the treatment was evaluated clinically and also by means of the Psoriasis Area Severity Index (PASI score). During this treatment, 434 patients (78.8%) became asymptomatic. Of 249 psoriatics receiving the conventional therapy, only 62 (24.9%) showed clinical recovery during the same period of time (P<0.05). The curative effect of bile acid supplementation was more pronounced in the acute form of psoriasis (95.1% of the patients became asymptomatic). Two years later, 319 out of the 551 acute and chronic psoriasis patients treated with bile acid (57.9%) were asymptomatic, compared to only 15 out of the 249 patients (6.0%) receiving the conventional treatment (P<0.05). At the end of the 2-year follow-up, only 10 out of 139 acute psoriasis patients (7.2%) receiving the conventional therapy and 147 out of 184 bile acid treated patients (79.9%) were asymptomatic (P<0.01).To conclude, the results obtained suggest that psoriasis can be treated with success by oral bile acid supplementation presumably affecting the microflora and endotoxins released and their uptake in the gut.