The effect of continuing penicillamine or gold treatment was examined in 53 patients with biopsy proven penicillamine (32) or gold (21) nephropathy. Thirty-two patients stopped penicillamine or gold treatment as soon as proteinuria was detected whilst 21 patients continued treatment for periods of 2-11 months. The 24-hour creatinine clearance and urinary protein excretion were measured serially for a median period of 6 years. No significant differences were observed in the initial or maximum proteinuria, the duration of the proteinuria or in the initial or latest creatinine clearances between the groups of patients. These results indicate that penicillamine or gold treatment may be continued for short periods under close supervision despite moderate proteinuria without causing permanent renal damage. As several alternative non-nephrotoxic agents are available for the treatment of rheumatoid arthritis, continued treatment with penicillamine or gold despite proteinuria is seldom indicated.