The argyrophilic staining (AgNOR) technique, novel in histopathology, was applied to a series of 20 non-Hodgkin's lymphomas (NHL) of established Kiel subtype. The method demonstrates nucleolar organizer regions (NORs) by virtue of sulphydryl groups on their associated proteins and the enumeration of AgNOR foci has been previously shown to discriminate between NHL of low- and high-grade histological types. This finding was confirmed and the results were compared with those obtained by means of DNA flow cytometry performed on paraffin wax-embedded tissue from the same lymphomas. There was a very good linear correlation between the mean numbers of AgNOR sites per nucleus and the percentage of S-phase cells for each case, both values being high in high-grade NHL and low in low-grade lesions. Conversely there was no significant correlation between the DNA index, representing DNA aneuploidy, and AgNOR counts. It is suggested that the numbers of AgNORs in a lymphoma may be related to the dividing fraction of cells rather than, as might be expected, to ploidy alone. It is also proposed that the AgNOR technique, which is rapid, simple, and inexpensive, may provide, at least, an adjunct to DNA flow cytometry in the assessment of neoplasm in histopathology.