Acid ceramidase is a lipid hydrolyase responsible for the degradation of ceramide into sphingosine and free fatty acids within lysosomes. It can also synthesize ceramide from sphingosine and free fatty acids as well. The reverse activity is pH dependent (6.0 vs 4.5, respectively). This suggests that the enzyme may have diverse functions within cells dependent on its subcellular location and the local pH. Recent studies have shown that acid ceramidase activity is aberrantly expressed in several human cancers and that it might be a useful drug target. As an example, inhibitors of enzyme activity have been shown to slow the growth of cancer cells alone or in combination with other established, anti-oncogenic treatments. Aberrant activity has also been shown in AlzheimerÕs disease and overexpression may prevent insulin resistant (Type II) diabetes by free fatty acids.