A multistep immunocytochemical method utilizing horseradish peroxidase as an immunologically bound marker was used to detect and localize IgA deposits in skin of patients with dermatitis herpetiformis at the ultrastructural level. IgA was found in the upper papillary dermis forming irregular aggregates in seemingly haphazard distribution. These aggregates were associated with microfibrillar bundles and with the microfibrillar component of the elastic tissue. IgA was also detected on anchoring fibrils, but showed no topical relationship to the basal lamina which was always spared. This finding indicates that basal lamina components do not serve as target sites for the immunologic reaction occurring in dermatitis herpetiformis. The selective affinity of IgA deposits to microbfibrillar bundles may be relevant to the hypothesis that the skin pathology in dermatitis herpetiformis is caused by circulating gluten-antigluten complexes, trapped in the skin by reticulin-bound antireticulin antibodies which cross-react with gluten.