Lipoprotein (a), (Lp(a)), an independent atherogenic factor, was significantly increased in 93 patients with classical, seropositive rheumatoid arthritis of median disease activity. In the patients with Lp(a) concentrations above the upper reference value of 480 mg/l there was a significant correlation between Lp(a) and the concentration of orosomucoid, erythrocyte sedimentation rate, and the platelet count. The plasma concentrations of cholesterol and high density lipoprotein-cholesterol in both male and female patients were significantly lower than in controls. Apolipoprotein B and apolipoprotein AI in the patients correlated significantly with total cholesterol and high density lipoprotein-cholesterol respectively.