We used Doppler sonography to evaluate the therapeutic effects of infliximab on the knee and metacarpophalangeal (MCP) joints of 10 patients with rheumatoid arthritis (RA), based on the color flow signals (CFS) and resistance index (RI) of synovial vascularity. After three injections of infliximab, we observed significant improvement in numbers of tender joints (P < 0.01), values of C-reactive protein (CRP) (P < 0.01), erythrocyte sedimentation rate (ESR) (P < 0.001), disease activity scores including tender joints, swollen joints, and ESR (DAS28-E3) (P < 0.0001), and CFS of knee (P < 0.001) and MCP (P < 0.05) joints. There was no significant improvement in RI values of knee or MCP joints after the therapy. We observed significant correlation between CFS of knee joints (knee-CFS) and values of CRP (P < 0.01), ESR (P < 0.01), and DAS28-E3 (P < 0.05), but not between CFS of MCP joints (MCP-CFS) and values of CRP, ESR, and DAS28-E3. However, no significant correlation was observed between 10 difference values (before values-after values) of CFS grades of knee or MCP joints and 10 difference values each of CRP, ESR, or DAS28-E3. The knee joints are more suitable than MCP joints for obtaining CFS in Doppler sonography, and are more useful than MCP joints for evaluation.