Most cases of hair loss are based on premature induction of follicle regression (catagen). Deciphering the unknown regulation of catagen is therefore clinically important, but catagen is also an excellent model for organ involution by rapid terminal differentiation and for epithelial cell death (apoptosis). We here report an assay for the controlled pharmacologic induction and manipulation of catagen follicles. Dexamethasone-21-acetate (0.1%) was applied once daily to depilation-induced, growing follicles (anagen VI) on the backs of C57 B1-6 mice. Characteristic catagen-associated changes in skin color were photodocumented and assessed by morphometric histology. Topical dexamethasone induced catagen-like follicles significantly earlier, more homogeneously, and also more extensively than vehicle. This process was inhibited by high intraperitoneal doses of cyclosporin A. In addition to its clinical relevance as a screening assay for catagen-blocking drugs, this simple murine model is an attractive tool for dissecting the molecular, cellular, and developmental biology of catagen.