ABSTRACT. Between the laminar epidermis and the laminar dermis of laminar region (LR) in equine foot, it can be observed the basement membrane zone (BMZ), which is composed of a basement membrane and its accompaniments like the hemidesmosome and anchoring fibril. Alteration in the BMZ in equine laminitis is possibly related with not only development but also recovery outcome and recurrence of this disease. However, there is little known about the structure of the BMZ during the recovery phase of this disease. To assess the condition of the BMZ of LR affected by chronic laminitis, the tissue was examined in three cases at two weeks, four weeks and three months after the onset of laminitis, using pathological, immunohistochemical and electron microscopic techniques. Histologically in all laminitis cases, there was a regenerated laminar epidermis with proliferating keratinocytes between the Stratum medium and the dermis, but it included the undeveloped secondary epidermal laminae (ud-SELs) structure in one side of the primary epidermal laminae, especially in the part of the deep area of LR. Immunohistochemical results were positive for the anti-type IV collagen, anti-type VII collagen and anti-laminin 5 antibodies in the most BMZs. However, partial BMZs adjacent to the ud-SELs were negative for the anti-type VII collagen and anti-laminin 5 antibodies. Ultrastructurally, in the BMZ of the ud-SEL, the lamina densa and the lamina lucida were present. In contrast, the anchoring fibrils and the hemidesmosomes were either absent, or present at lower than normal levels. In conclusion, the present study indicated that the part of regenerated LR in chronic laminitis was not able to fully restore to construct the BMZ for a long time, especially in the unilateral side of laminar epidermis. It might be related with recurrence of this disease. KEY WORDS: basement membrane zone, chronic laminitis, collagen, equine, laminin 5.J. Vet. Med. Sci. 67 (7): [685][686][687][688][689][690][691] 2005 The integumental tissues of the foot are important in supporting the horse's entire body weight during static and dynamic loading conditions. If severe intractable hoof disease occurs, the horse may lose not only the ability to run, but also to stand. Laminitis is one such intractable hoof condition and has a recurrent nature. Many horses have suffered from this disease over extended periods, resulting in significant treatment costs, and therefore the equine industry has a great deal of interest in clarifying the pathogenesis and developing treatment methods [5,9,12].Anatomically, the laminar region in foot displays a complex 3-dimensional structure consisting of the primary epidermal lamina (PEL) and the secondary epidermal lamina (SEL) which interdigitate with their dermal counterparts [24]. These dermal and epidermal components are separated by the basement membrane zone (BMZ), which is composed of a basement membrane and its accompaniments like the hemidesmosome and anchoring fibril [23]. The hemidesmosome, anchoring fibril and other c...