The yeast contaminating the starter cultures of Saccharomyces cerevisiae fermentation strains BSP 1-4, used in the Turkish baking industry, was identified as Candida tropicalis with a killer phenotype. The activity of the killer toxin against the industrial strains was optimum at pH 3.9 and 4.1 at 22-25 degrees C. The activities of some killer toxin-producing yeasts of known phenotypes against C. tropicalis were determined. Among the yeasts tested S. cerevisiae K3 and Hansenula anamola K8 were inhibitory to C. tropicalis. This led to a conclusion that K8 and/or K3 killer traits could be used for the construction of industrial strains resistant to C. tropicalis contamination. (C) 1997 Academic Press Limited.