A total of 1833 out of over 16,000 'initial' isolates of Mycobacterium tuberculosis, submitted by hospital laboratories to the PHLS Regional Tuberculosis Centres in England and Wales between 1982 and 1991, were resistant to one or more first line anti-tuberculosis drugs. Isoniazid resistance was found in 6.1% of these strains, half of which were resistant to isoniazid alone. Resistance to isoniazid and rifampicin, with or without resistance to other drugs, was found in 0.6% of isolates. The proportion of initial isolates resistant to one or more drugs was 9.8%. It ranged from 8.0% to 10.9% between 1982 and 1990, and increased to 14.2% in 1991. The incidence of multiple drug resistance remained very low throughout the period. However, in the light of the problems with tuberculosis and drug resistance emerging elsewhere in the world, vigilance is essential, and enhanced surveillance is being planned in England and Wales.