Serum antibody titres to Adenovirus, Chlamydia Group B, Coxiella burnettii, Cytomegalovirus, Herpes simplex virus, Influenza A, Influenza B, Measles and Mycoplasma pneumoniae were measured in 33 patients with a clinical diagnosis of Alzheimer's disease, and in 28 non-demented controls suffering from functional psychiatric disorders. No statistically significant differences were found between the patients and controls, and it is concluded that these agents play no role in the aetiology of Alzheimer's disease.