The purpose of this study was to determine whether low-dose methotrexate pulse therapy, which had recently become important in the treatment of rheumatoid arthritis, was effective for controlling the progression of articular destruction in rats with adjuvant arthritis. Intraperitoneal methotrexate at a dose of 0.05 or 0.1 mg kg-1 twice weekly inhibited inflammation in rats with adjuvant arthritis, as shown by reduction of the hind-paw volume. Methotrexate also inhibited articular destruction, as shown by X-ray findings. Although the mechanisms by which low-dose pulse methotrexate acts on rat adjuvant arthritis are still unclear, our results imply that it might effectively slow the progression of articular destruction in rheumatoid arthritis in man. In addition, assessment of articular destruction in this animal model might be useful when evaluating new treatments for rheumatoid arthritis.