Primary or acquired drug resistance is well recognized as a common cause of treatment failure of patients with cancer. From a rheumatoid arthritis (RA) perspective, the issue of resistance to anti-rheumatic drugs (e.g. disease-modifying anti-rheumatic drugs [DMARDs]) has not received much attention. A possible mechanism of drug resistance is overexpression of multidrug resistance (MDR)-related proteins. The objective of this study was to identify whether various MDR proteins are expressed on macrophages as potential target cells for DMARDs.