16 patients with classical rheumatoid arthritis (RA) selected at random underwent fasting for 7--10 days, followed by a 9-week period on a lactovegetarian diet. 10 RA patients acted as controls, taking normal diet. Pain, stiffness, medication, and clinical and biochemical findings were recorded before fasting, on the first day after the conclusion of the fasting period, and at the end of the lactovegetarian period. After fasting, 5 of 15 patients showed objective signs of improvement, compared with only one of the controls. The fasting patients showed reduced pain, stiffness, consumption of analgetics, several clinical variables, and serum concentration of orosomucoid. At the conclusion of the lactovegetarian diet period only one Diet patient showed objective improvement. No differences were found between the Diet patients and the controls concerning symptoms, drug consumption, or clinical and biochemical variables. We conclude that fasting may produce subjective and objective improvements in RA, though of short duration, but the findings of this investigation do not indicate that lactovegetarian diet has any beneficial effects.