Patients suffering from anorexia nervosa rarely appear to develop the common cold or influenza. This study examines the immunological response of fifteen female anorexia nervosa patients of both the vomiting and carbohydrate-abstaining type and compares them with a control population matched for age and occupation. Both anorectics and control populations received the admune influenza vaccine. Initially both groups had similar haemagglutination inhibition titres against the three different viral antigens: A/HK; A/PC; A/Eng. However, the anorectics showed over a 2-month period a higher titre of antibody especially to the Hong Kong virus: this was sigignificant. Cellular immune responses were measured using a tuberculin and a macrophage inhibition test, no significant difference between the two groups was obderved. These results which support the clinical findings are discussed.