…Our results demonstrate that caspases are expressed in discrete areas of the hair follicle and may control the hair loss andhair regrowth cycle. It appears that all the caspase family members are expressed in normal cells in an enzymatically inactive pro-form, and that upon the onset of apoptosis they are converted to an enzymatically active processed form via a poorly understood mechanism involving either oligomerization, self-proteolysis or cleavage by another family member or both. All members of the protease family show an extremely high prefe-rence for cleavage of their substrates after an aspartyl residue at the P1 position. Once activated, caspases are sensitive to inhibition by the viral products CrmA and p35, and perhaps more significantly from the point of normal regulation, by endogenous inhibitors, X-linked inhibitor of apoptosis (XIAP).