Genetic analysis of venturicidin-resistant mutants has revealed the presence of both nuclear and mitochondrial genes responsible for determining venturicidin sensitivity/resistance in Saccharomyces cerevisiae. Recombination studies show that the mutation with phenotype VENR is situated at mitochondrial locus OL I and is therefore extremely useful of future genetic manipulations as it gives a unique phenotype to this locus distinguishable from the second oligomycin locus OL II. The mutations with phenotype VENR OLYR are linked to oligomycin locus OL I and have been allocated a new mitochondrial locus, namely OL III. Three factor croses involving the venturicidin mutations at loci OL I and OL III have shown them to freely recombine with the other mitochondrial loci R I, R III and OL II. The mitochondrial genetic map is therefore represented as four 'recombinational linkage groups'. A fifth linkage group is also specified for mutants with phenotype VENR TETR, and is probably located on a separate DNA molecule from the four other groups.