In 15 patients with rheumatoid arthritis who were in clinical remission the weekly regimen of methotrexate treatment was changed to fortnightly without a change in dose. A total of 13 patients completed a 12 month trial. No change in clinical or laboratory parameters occurred. There was no change in the use of analgesics or non-steroidal anti-inflammatory drugs and the patients remained in remission. Two patients had to be withdrawn after two and four months respectively because of a flare in disease activity. It is suggested that in most patients with rheumatoid arthritis who are treated with methotrexate and whose disease activity is stable a fortnightly regimen can be permitted without affecting drug efficacy.