The anatomy of the epidermis, dermis and subcutaneous tissues of the nail apparatus is distinct from that of non-appendageal skin. Apart from the demonstration of the longitudinal configuration of the dermal-epidermal junction of the nail bed, there have been no studies of the composition of the basement membrane zone of the nail apparatus. We obtained three human accessory digits, including one thumb, all of which had been amputated for cosmetic reasons, and were without known pathology. Specimens were stained with a battery of monoclonal and polyclonal antibodies which target normal basement membrane zone antigens, and studied by indirect immunofluorescence. This study demonstrated that the four distinct regions of the nail, namely the proximal nail fold, the nail matrix, the nail bed and the hyponychium expressed all the target antigens found in the normal non-appendageal basement membrane. In particular, there was normal expression of the epidermal-associated antigens, the 220- and 180-kDa bullous pemphigoid antigens, and the alpha 6 beta 4 integrin. There was also normal expression of the lamina lucida antigens LH39, GB3 and laminin. It is of interest that the dermal-associated components, namely the 285-kDa linear IgA antigen, the extracellular matrix glycoproteins chondroitin sulphate, type VII collagen and its closely associated proteins, and the poorly characterized antigen for LH24 and LH39 were all normally expressed. Fibronectin, which is not a normal basement membrane zone component, was diffusely expressed in the extracellular matrix, but did not accentuate the basement membrane zone.(ABSTRACT TRUNCATED AT 250 WORDS)