β-Xylosidase activity has been detected in cell-free extracts and in culture fluids when Cryptococcus albidus var. aerius was grown on glucose as the sole carbon source. The enzyme appears to be constitutive. Mild acid treatment of whole cells suggested that the total activity is located in the periplasmic space and some experiments indicated that it is partially associated with the cell walls. DEAE-Sephadex A50 chromatography has shown that there are two different forms of β-xylosidase in the cell-free extracts, but only one form is present in the supernatants of culture.