The porcine adenovirus NADC-1 isolate, a strain of porcine adenovirus type 4, has a fibre with an atypical architecture. In addition to a classical virus attachment region, shaft and head domains, it contains an additional galectin like domain C-terminal to the head domain and connected to the head domain by a long RGD-containing loop. The galectin-like domain contains two putative carbohydrate-recognition domains. The head and galectin-like domains have been independently crystallized. Diffraction data have been obtained to 3.2 angstrom resolution from crystals of the head domain and to 1.9 angstrom resolution from galectin-like domain crystals.