The number of NK T cells was measured in relation to the Th1/Th2 imbalance observed in RA. Peripheral blood samples of patients with RA (n = 60) and healthy controls (n = 36) were stained with anti‐NK receptor 1A (anti‐NKR‐P1A), anti‐CD56, and anti‐CD3 MoAbs, and examined by three‐colour flow cytometry. NK T (NKR‐P1A⁺CD3⁺) cells in the peripheral blood were decreased in RA compared with the controls: 25 ± 20/μl versus 143 ± 53/μl (P < 0.0001). CD56⁺CD3⁺ cells were also decreased in RA: 60 ± 46/μl versus 116 ± 54/μl (P < 0.0001). The decrease was significant when adjusted to the number of total lymphocytes (P < 0.0001) or NK (CD56⁺CD3⁻) cells (P < 0.0001), and showed no correlation with age, sex, disease duration, disease activity, functional class, x‐ray stage, drug treatment, joint score, grip strength, C‐reactive protein, rheumatoid factor or erythrocyte sedimentation rate of the patients. The results show that the levels of NK T cells are depressed in the peripheral blood of patients with RA, suggesting that the measurement of NK T cells in peripheral blood may have clinical importance for a Th1‐type autoimmune disease like RA.