Results of experiments on the Mir space station (EO-25 and EO-26) demonstrated that the conditions of orbital flight, primarily the cosmic radiation, was a mutagenic factor affecting both the genotype and phenotype of an oil-oxidizing bacterial strain, Mycobacterium flavescens EX-91. The emerging mutants differed from original culture by the rate of colony growth and the ability to ferment certain carbohydrates or synthesize beta-galactosidase. Changes in the rate of utilization of raw oil and individual hydrocarbon types (constituting model mixtures) suggest that cosmic radiation may serve as a means of obtaining mutant clones of microorganisms with new properties.