During a total population survey of viral hepatitis in the London Boroughs of Hounslow, Richmond and Ealing, 784 patients were seen in three years from 1 March 1972 to 28 February 1975. A diagnosis of viral hepatitis was accepted in 489. The annual incidence was 24 per 100 000. 455 of the patients were tested for the hepatitis B surface antigen (HBsAg) by a radioimmunoassay technique and 93 (20 per cent) of these were positive. The majority of the patients with typc B hepatitis were in their third or fourth decades. None was under the age of 16. The male to female ratio among patients with hepatitis B was 2 to 1 in those under the age of 30 and 5 to 1 in those aged 30 and over. The seasonal distribution of viral hepatitis showed a peak in the spring, solely from an increased incidence of non-B hepatitis, and a second, smaller peak in the autumn. There was no appreciable clustering of patients except for one local outbreak in a housing estate during the first year affecting mainly children going to the same primary school, and their parents. Patients with hepatitis B had a longer pre-icteric illness (p < 0·05), greater duration of jaundice (p < 0·001) and higher peak levels of serum bilirubin (p < 0·0005) and sernum alanine amino transferase (A1 T) (p < 0·03) than patients with non-B hepatitis. The finding of the surface antigen was also associated with a higher frequency of skin rash (p < 0·0005) and a greater duration of arthralgia (p < 0·03). Among the HBsAg negative patients the incidence of arthralgia increased with age (p < 0·0005). Abdominal pain (p < 0·005) and vomiting (p < 0·005) were more common in the young. The injection experience of patients with hepatitis B showed a high proportion of ‘nontherapeutic’' exposure such as drug addiction. Significantly more HBsAg positive men were single than in the local community (p < 0·0001) or among the HBsAg negative men (p < 0·01). There was no significant difference between the proportions of single women among the antigen positive and negative patients. Many of the HBsAg positive single men were either known to be or strongly suspected of being homosexual. The ad subtype of the HBsAg was found more often in males (p < 0·01), particularly over the age of 30. All eight drug addicts tested for subtype were ay, as were two non-addicted female consorts. The association between addiction and ay subtype was highly significant in the males (p < 0·001). Tbc ad subtype was found in an 11 of the admitted homosexual HBsAg positive men and in all but one of the 17 strongly suspected of being homosexual.

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