Epidermis from seven sites of Acorn barnacle (Semibalanus balanoides) attachment on humpback whales (Megaptera novaeangliae) were evaluated for types and degree of tissue reaction. In all cases, there was marked epithelial hyperplasia with fronds of epithelium sandwiched between calcareous plates. Epithelium in these regions exhibited marked hydropic swelling. Attenuation and separation of the stratum basale by eosinophilic proteinaceous material was also a common finding. Inflammation was not evident. The host response to adhered Balanomorpha is localized to the epithelium. Tissues for this study were collected under a Letter of Authorization from NOAA Fisheries to the UNCW Marine Mammal Stranding Program.