A screening of lignin-degrading basidial fungi that can grow in the presence of thiomorpholine derivatives (the mixture of 1,4-perhydrothiazines) has been performed. Strain Bjerkandera adusta VKM F-3477 was shown to have the maximal rate of growth in the presence of these compounds, and its capacity for thiomorpholine degradation was studied. The methods of quantitative analysis of thiomorpholine and its degradation products on the basis of thin layer chromatography and high-performance liquid chromatography were developed. It was shown that the B. adusta strain did not utilize thiomorpholine as a carbon source but transformed it into thiomorpholine sulfoxide that accumulated in the medium. Mn peroxidase produced by B. adusta in the course of thiomorpholine transformation is not directly involved in its oxidation.