Low-dose methotrexate has gained widespread acceptance as a second-line agent in rheumatoid arthritis (RA). The Leeds Human Model Screening System (LHMSS) is a validated screening mechanism allowing the rapid evaluation of compounds for their potential as anti-rheumatic agents, the results of which have been confirmed in longer term studies. We have evaluated methotrexate in patients with RA using the LHMSS at a maintenance dose of 10mg/week. Significant change occurred in four out of eleven variables over a 24-week period (p < 0.01). This degree of change is greater than that seen with nonsteroidal anti-inflammatory agents but less than with other recognised second-line agents such as D-penicillamine, suggesting that methotrexate may have less potential as a second-line agent than D-penicillamine.