During February, 1983, an outbreak of an unusual febrile illness occurred in over 130 children attending a boarding school in Chelmsford, Essex. The clinical features included fever, an erythematous rash that was most prominent on the hands and feet, arthralgia, and the subsequent development of a sore throat. The nature and distribution of the rash varied considerably between patients and at different stages of illness. At first a viral aetiology was regarded as most likely. When Streptobacillus moniliformis was later isolated from the blood of 4 of the patients with moderately severe illnesses it became apparent that an outbreak of Haverhill fever had occurred at this school. The most probable source of the outbreak was raw milk, since all 4 patients had consumed raw milk at the school shortly before the onset of symptoms and there was no evidence of person-to-person spread of infection.