Using a silver staining technique, nucleolar organizer region-associated proteins (Ag-NORs) have been studied in paraffin sections of 90 non-Hodgkin's lymphomas, five palatine tonsils and five 'reactive' lymph nodes. The method was readily applicable to these preparations and the Ag-NORs were enumerated with ease. A significant difference was found between the numbers of Ag-NORs in the nuclei of low-grade lymphomas (from a mean of 1 to 1.5 per nucleus) and those of high-grade lymphomas (a mean of 4.4 to 6.8 per nucleus). The Ag-NOR regions were often observed in nuclei in areas where nucleoli themselves were not visible. It is suggested that this method, previously largely the province of the cytogeneticist, should find widespread applications in the field of tumour histopathology.