Patients with rheumatoid arthritis were found to have elevated urinary copper excretion rates. They also had increased serum levels of coeruloplasmin and presumably also of a non-coeruloplasmin copper fraction. The zinc levels in serum and urine did not differ significantly from control values. Serum selenium and serum iron were decreased as compared with those of the healthy controls. It is suggested that an increased copper-to-selenium ratio may be of pathogenetic signficance. Biochemical changes induced by copper may be antagonized (at least partly) by the treatment with gold thiomalate and D-penicillamine. If serum selenium deficiency in RA can be confirmed in larger materials, selenium supplementation as a therapeutic measure should be considered.