The incidence of infections caused by Yeasts has increased in recent years due to increases in the number of immuno- compromised patients (e.g. AIDS). Because Yeasts grow slowly, it is difficult but important to develop rapid methods for their identification. Biolog holds two patents on a new redox method which identifies an organism based on patterns of carbon source utilization. The method, employs a tetrazolium dye to colorimetrically indicate carbon source oxidations. Principal advantages of the method are: (1) speed--for most microorganisms tests can be completed in under 4 hours, (2) simplicity--this is an easy to inoculate and read single color chemistry, and (3) accuracy--drawing from thousands of potential carbon sources should enable us to develop a test panel that is far more accurate than anything presently available. This Phase I study will demonstrate the feasibility of developing a rapid and accurate speciation kit for Yeasts. Two tasks are involved: (1) the development of a suspension medium compatible with the redox chemistry which is tailored to this diverse group of Yeasts, and (2) a survey of 380 potential test substrates to demonstrate that new and useful speciation tests can be found based on carbon source oxidation reactions. The potential market for these kits is large, and includes hospital, public health, and clinical laboratories.