Formation of a D-penicillamine-copper complex may be necessary for the anti-rheumatic effect of D-penicillamine. Thus, depletion of copper stores by D-penicillamine may eventually lead to relapse in D-penicillamine treated patients. Twenty-one patients who relapsed on D-penicillamine were randomised to copper sulphate 20 mg daily (n = 13) or matched placebo (n = 8) in addition to penicillamine daily for 16 weeks. Urinary copper was increased in the copper treated patients but no statistically significant or clinically important improvement occurred in either group.