Blood eosinophil levels were examined in 200 (100 mild and 100 severe) patients with atopic dermatitis. Eosinophil levels roughly correlated with disease severity. However, the pattern of eosinophilia was not homogeneous. Very high eosinophil counts were common in severe cases of atopic dermatitis who had a personal or family history of respiratory atopy, while normal or moderately elevated eosinophil values were obtained in severe cases of 'pure' atopic dermatitis who had neither personal nor family history of respiratory atopy. It is suggested that disease severity and personal or family history of respiratory atopy are important factors in determining high blood eosinophil levels in atopic dermatitis.