Human hair follicle mesenchyme contains a distinctive extracellular matrix which varies in volume and composition in concert with the hair growth cycle. To investigate the possibility that mesenchymal function is disturbed in alopecia areata we have studied the expression of extracellular matrix constituents in scalp biopsies from 14 patients by immunohistochemical staining for basement membrane proteins, proteoglycans and interstitial collagens. The staining patterns in follicles from non-lesional scalp were normal. Miniature anagen follicles from bald patches also showed relatively normal expression of basement membrane proteins and proteoglycans. However, in some large anagen follicles from lesional sites, there was loss of the normal staining pattern for chondroitin-6-sulphate in the dermal papilla. In lesional catagen follicles, the glassy membranes showed marked convolution and thickening. These structures stained strongly for laminin and type IV collagen but only weakly for interstitial collagens.