This software publication is a revision of the text on Yeasts by Barnett, Payne and Yarrow entitled Characteristics and Identification, published by the Press in 1983. Researchers can input results of tests they have carried out on a particular strain of yeast, and the program will list all the possible yeasts that would give the input results. Further, the program will produce a list of tests necessary to distinguish those yeasts on the list of possible yeasts. A comprehensive set of data of the highest quality (the authors are leading researchers in the field) has been made available in a format which allows great accessibility, is highly usable and much more quickly exploited than in alternative media. The software will be published initially in three versions, the IBM-PC, the DEC Rainbow using both MS-DOS and CP/M and the superbrain using CP/M. Each package will contain a 51/4 inch floppy disc carrying the program, written in FORTRAN, a user's manual and a leaflet of operating instructions which would be specific to each type of computer.