The use of eight rapid tests for the identification of 1307 strains of mycobacteria belonging to 18 species was evaluated. The standard niacin, nitrate-reductase and catalase tests were supplemented by new tests for the detection of beta glucosidase, urease, penicillinase, trehalase and cephalosporinase. This combination of eight rapid tests was not able to replace more conventional procedures but in some cases was of value in discriminating between closely related species.