Between 1990 and 1999, 182 men were treated for non-seminomatous germ cell testicular tumours. In 24 of them after chemotherapy a residual retroperitoneal mass was removed. In 14 of them additional immunohistochemical (IHC) examinations using antibodies against cytokeratins, vimentin, PLAP, CD30, AFP, βhCG, p53, and MIB-1 were performed. We compared the results of those additional studies with the results of routine histopathological examination. Histological assessment revealed most frequently (ca. 54% of cases) non-neoplastic lesions, i.e. fibro-cystic, necrotic or inflammatory tumours and lymphatic tissue. In about 33% of cases, surviving live neoplastic cells were found.