Tuberculosis is a major public health problem which has been compounded by the emergence of multi-drug-resistant strains of Myco. tuberculosis (MDR-TB), an increased use of immunosuppressive therapy and increasing numbers of HIV infection. To further complicate the infection control issues, many of the environmentally associated mycobacteria, commonly referred to as opportunistic pathogens, are being incriminated in human infection with increasing frequency. Information is required on the mycobactericidal effectiveness of disinfectants, especially those associated with heat sensitive equipment such as bronchoscopes, which may be contaminated with mycobacteria. The activity of disinfectants against Myco. tuberculosis is well documented. However, there is much variation in test methodology resulting in conflicting efficacy data. Therefore a standard, reproducible and practical method must be developed which will give useful and reliable data on the resistance of Myco. tuberculosis and other mycobacteria of increasing clinical importance to current disinfection procedures. A standard test method was developed for use in this study. Suspension and carrier tests were carried out in the presence and absence of 10% serum as the organiC load. The test organisms were type strains of Myco terrae, Myco chelonae, Myco. fortuitum and Myco. tuberculosis. 1\vo endoscope washer disinfector isolates of Myco. chelonae and a clinical isolate of Myco. avium-intraceUulare were also used. The type strains of Myco. chelonae and Myco. fortuitum were very sensitive to all disinfectants tested. My co. terrae was slightly more resistant than Myco. tuberculosis. This is in agreement with published data. Myco. avium-intraceUulare was without doubt the most resistant of all the test organisms. The two machine isolates of Myco. chelonae were extremely resistant to 2% glutaraldehyde. This prompted further work to assess if these two strains differed from the type strain in other ways.