Anhydrous and crude glycerols were bioconverted to citric acid by using Aspergillus niger mould strains. After screening of 19 strains in submerged batch cultures, in flasks, in a shaking incubator the A. niger PD-66 strain with the highest yield and efficiency, was selected and used in the study. The highest final concn. of citric acid (86.11 g/dm(3)), the highest volumetric reaction rate (0.465 g/(dm(3)h)) and the most favourable citric acid biosynthesis efficiency coeff. (40.10%.g/(dm(3).h)) were obtained in cultures with anhydrous glycerol. Crude glycerol showed significantly lower productivity and efficiency of citric acid prodn.