Genetically useful strains of the hydrocarbon-utilizing yeast Saccharomycopsis lipolytica were developed through extensive inbreeding. Spore viability and the percentage of 4-spored asci were increased to the point where tetrad analysis was possible. Procedures for mutant isolation and scoring, maintenance of stocks, mating, sporulation, complementation, tetrad and random spore analysis have been developed for these inbred strains. Sixty seven mutations in fiftyeight genes have been isolated and utilized in mapping studies. Twenty-two cases of linkage have been detected among the 278 gene pairs investigated. Six linkage fragments have been established and a few genes ordered in these fragments. No centromere, linked markers have yet been detected. Evidence for gene conversion, mitotic recombination and diploidization in S. lipolytica is presented.