Five cases of gastric carcinoma of undifferentiated (gastric) type containing Paneth-like cells were studied by immunoelectron microscopy for lysozyme using two methods. The Paneth-like cells in these carcinomas had lost their cellular polarity and possessed electron-dense granules. These granules varied in size (0.5-3 micron in diameter), electron density and shape. Post-embedding method revealed immunolocalization of lysozyme in these granules in all cases, similar to that in normal Paneth cells. Pre-embedding method showed immunoreactivity diffusely or focally located in the cytoplasm, but this approach was unable to reveal immunoreactivity in the granules, a feature also common to normal cells. Our study therefore confirmed that Paneth-like carcinoma cells and normal Paneth cells had the same features, and indicated that undifferentiated-type gastric carcinoma could possess specially differentiated cells, providing further support that such carcinoma could express multipotentiality. The difference in the results obtained by the two immunoelectron microscopy methods was discussed.