Spleens and lymph nodes fixed lightly for optimal immunocytochemistry or processed routinely for surgical diagnosis disclosed strong selective immunostaining for IgG in numerous immunocytes in tumor-free areas. Areas involved by Hodgkin's disease revealed, in addition, strong immunostaining for IgG but not IgM in Reed-Sternberg cells and faint to strong staining in Hodgkin cells as well. Ultrastructurally the Reed-Sternberg and Hodgkin cells displayed abundant polyribosomes and sparse granular reticulum and appeared to form unexportable IgG on unbound ribosomes.