The data about cytoplasmic control of toxin formation in Saccharomyces paradoxus CBS5829 are presented. A novel determinant (KIL-k3) is probably located in the mitochondrial genome. In other mutations, adenine deficiency results in suppression of toxin formation of the K3 type. A new killer plasmid (KIL-kx) was detected in Sacch. paradoxus VKM Y-2472.