The products of hyaluronan digestion by hyaluronidase PH-20 inhibit oligodendrocyte progenitor cell (OPC) maturation in demyelinating lesions, leading to failure of remyelination, new research shows. PH-20 was found to be upregulated in demyelinating lesions in both mice and humans, and inhibition of this enzyme promoted OPC maturation in cell culture and in the mouse brain. The authors propose that PH-20 could be a therapeutic target in demyelinating diseases such as multiple sclerosis.