Twenty patients with arthritis and various skin diseases were studied on a metabolic ward during a 2-week period of modified fast followed by a 3-week period of vegetarian diet. During fasting, arthralgia was less intense in many subjects. In some types of skin diseases (pustulosis palmaris et plantaris and atopic eczema) an improvement could be demonstrated during the fast. During the vegan diet, both signs and symptoms returned in most patients, with the exception of some patients with psoriasis who experienced an improvement. The concentrations of lactoferrin in serum reflect the turnover and activity of neutrophil leukocytes. When this protein was initially increased it fell to normal values in most cases. The improvement or impairment of signs and symptoms was related to the lactoferrin levels in serum.