Rabbit antibodies were produced in response to cholesterol induced chicken atheroma and chicken normal intima. Properties of these antisera were studied by complement fixation and described by isofixation curves. It was found that anti-atheroma sera reacted best with atheroma antigen and in addition reacted well with a wide variety of other chicken tissues. Anti-normal intima sera reacted well with either intima or atheroma antigen and had a limited spectrum of reactivity with other tissues. In vivo activity of these antisera could not be demonstrated.