A retrospective review of 4405 patients' charts identified 214 patients who initiated antimalarial therapy between January 1987 and April 1993 for different rheumatic disorders (mean duration of therapy of 17 months). From these, three patients with myopathy were found for a total of 303 patient-years of therapy, for an incidence of 1 in 100 patient-years (95%, confidence interval 0.2-3). All three patients had rheumatoid arthritis and had received chloroquine for between 12 and 18 months with a maximum dose of 250 mg/daily. All had a muscle biopsy, but only one showed the classical rimmed vacuoles. All patients improved within 2 months after the drug was stopped. A review of the literature was carried out with special reference to the significance of clinical myopathy with a negative biopsy. We found that positive biopsies are usual only if the duration of symptoms have been allowed to persist for more than 6 months.