The incidence of methicillin-resistant Staphylococcus aureus in England and Wales was monitored by a weekly reporting scheme from early 1986 to March 1990. Potential coverage was approximately two-thirds of hospital beds. Reporting centres fell from a peak of 210 in 1986 to a low of 101 centres early in 1989 with later recovery. There were 2367 positive reports in 1986, 2174 in 1987, 1700 in 1988, 1701 in 1989 and 632 in the first quarter of 1990. Colonizations outnumbered infections by 2:1. There were marked regional differences: North-East Thames was dominant in 1986 and 1987, and then declined; South-East Thames showed a dramatic increase in 1988 which continued. Other regions showed less significant changes but there were continuing problems in the South-Western Region and in the West Midlands. Some of these changes were related to the decline of EMRSA-1, possibly due to the introduction of effective control measures, and to the emergence of EMRSA-3 in South-East Thames and its spread to Wessex.