SUMMARY An unlabelled antibody peroxidase-antiperoxidase method for the detection of IgG, IgM, complement (C3 and Clq), fibrinogen and albumin was applied to routinely processed paraffin sections of lung from 27 cases. The results in 11 cases were compared with those obtained by immunofluorescence using frozen sections. Tissue was obtained from surgical specimens of cases with interstitial pneumonia comprising 10 of the usual type (UIP) and three of the desquamative type (DIP). Tissue was also obtained from the specimens of cases with sarcoidosis (two cases) and granulomatous inflammation of unknown cause (one case).There were 11 control cases, nine with primary carcinoma of the lung and two with metastatic tumours of the lung.Immunoglobulins of various types and complement were seen in diseased lung tissue. Although most of these deposits were probably due to a non-immunological mechanism there was evidence of the possible implication of immune complexes in three cases of UIP and in the interstitial pneumonia present in the two cases of sarcoidosis.The immunoperoxidase technique is a more sensitive method than immunofluorescence and has the additional advantage of the easy identification of the precise sites of the various deposits.

A testicular malignant teratoma containing embryoid bodies and other embryonic and extra-embryonic structures in various stages of development has been examined by several histochemical and immunohistological techniques to study the distribution of various substances in the teratomatous elements. The substances demonstrated included various types of mucins; argyrophil, argentaffin, Paneth cells and haemosiderin granules; alpha-fetoprotein, alpha-l-anti-trypsin, lysozyme, beta-HCG and CEA. The significance of the findings is discussed in relation to early embryonic development.