We have used cytoduction and protoplast fusion to characterise the killer trait in Torulopsis glabrata. Killer trait could not be transferred by cytoduction to a non-killer strain of T. glabrata suggesting that the determinant(s) is/are not present in the cytoplasm. Consistent with this interpretation is the observation that all fusion products, where chromosomes of both the parents are represented, are killers. Non-killer segregants could be isolated from fusion products after treatment with benlate suggesting that loss of the trait is associated with non-disjunction and loss of a chromosome.