Confirmed acute hepatitis B infections are reported to the Public Health Laboratory Service Communicable Disease Surveillance Centre by laboratories in England and Wales. These reports have been used to monitor trends in the incidence of hepatitis B virus (HBV) infection over time, and between exposure categories and age groups. Between 1985 and 1996 a total of 9252 cases of acute HBV infection were reported; the number of reports fell from 1761 in 1985 to 581 in 1996. Most infections were reported in adults aged 15-44 years [n = 7365 (80%)], and infections were more commonly reported in males [n = 6490 (70%)] than females [n = 2658 (29%)]. The probable means of acquisition was known for just over half of all adult cases [4827/8956 (54%)]. Injecting drug use was the most common exposure [n = 1901 (21%)], followed by sex between men and women [n = 1140 (13%)] and sex between men [n = 1025 (11%)]. The number of infections in injecting drug users fell in the late 1980s, but increased again from 1991 onwards. In children aged under 15 years, infections acquired by mother to baby transmission accounted for 35/170 (21%) of the total. Surveillance indicates that the incidence of acute hepatitis B infection fell in the late 1980s, probably reflecting changed behaviour in injecting drug users. An increase in the number of infections in injecting drug users since 1993 may indicate ongoing transmission that has not been contained by the introduction of needle exchange schemes or by selective vaccination.