Objective. To investigate the effects of doxycycline on disease activity and joint destruction in patients with rheumatoid arthritis (RA). Methods. A 36 week double blind, placebo controlled crossover trial was conducted. Patients (n = 66) received 50 mg doxycycline or placebo twice a day during 12, 24, or 36 weeks. Patient assessments were performed before the treatment was administered, at 6, 12, 24 and 36 weeks of treatment, and finally at 4 weeks after cessation of treatment. Patient assessments, swollen and tender joint counts, duration of morning stiffness, erythrocyte sedimentation rate, and Modified Disease Activity Score were used as measures of disease activity. Effects on joint destruction were assessed by urinary excretion of the pyridinolines hydroxylysylpyridinoline and lysylpyridinoline and by scoring radiographic damage of hands and feet before and after treatment. Results. The changes of clinical or laboratory disease activity measures, pyridinoline excretion, or progression of radiographic joint damage during doxycycline or placebo treatment did not differ significantly. Conclusion. The results indicate that 50 mg doxycycline twice a day provided no therapeutic benefit for patients with RA.