The reactivity of eleven ‘tobacco smoke sensitive’ and eight ‘non-sensitive’ individuals to tobacco leaf allergens was tested by Crossed Radioimmunoelectrophoresis (CRIE). All nineteen study subjects had IgE antibodies to tobacco leaf antigens as measured by Radioallergosorbent Test (RAST) and seventeen of the nineteen individuals were atopic. Of the thirty-seven tobacco leaf precipitins detected by Cross Immunoelectro-phoresis (CIE), three were identified as allergens by CRIE. All nineteen subjects reacted to at least one of the three allergens detected. However, neither the intensity nor the incidence of reactivity with any of the three allergens correlated with smoking or ‘smoke sensitivity’.