Sterigmatomyces elviae DSM 70852 produced 12 g/l (S)-1,2,4-butanetriol (enantiomeric excess >99.9%) from 20 g/l racemate in 82 h. From the results of the inversion of an (R)-isomer to an (S)-isomer and GC-MS, it was suggested that (R)-1,2,4-butanetriol is oxidized to 1,4-dihydroxy2-butanone, which is reduced to an (S)-isomer.