Background: Chemotherapy-induced alopecia (CIA) has a devastating cosmetic effect, especially in the young. Recent data indicate that two major basement membrane components (laminin-332 and -511) of the skin have opposing effects on hair growth. Objective: In this study, we examined the role and localization of laminin-332 and -511 in CIA. Methods: We examined the expression of laminin-332 and -511 during the dystrophic catagen form of CIA induced in C57BL/6 mice by cyclophosphamide (CYP) treatment. Results: Our data indicate that both laminin-332 and its receptor α6β4 integrin are up-regulated (both quantitatively and spatially) after mid to late dystrophic catagen around the outer root sheath (ORS) in the lower third of hair follicles in CIA. This up-regulation also occurs at the transcriptional level. In contrast, laminin-511 is down-regulated after mid dystrophic catagen at the protein level, with transcriptional inactivation of laminin-511 occurring transiently at the early dystrophic catagen stage in both epidermal and ORS keratinocytes. Laminin-511 expression correlates with expression of α3 integrin in CIA and we also demonstrate that laminin-511 can up-regulate the activity of the α3 integrin promoter in cultured keratinocytes. Injection of a laminin-511 rich protein extract, but not recombinant laminin-332, in the back skin of mice delays hair loss in CYP-induced CIA. Conclusions: We propose that abrupt hair loss in CIA is, at least in part, caused by down-regulation of laminin-511 and up-regulation of laminin-332 at the transcriptional and translational levels.