The activity of nucleolar organizer regions (Ag-NORs) and the frequency of NOR associations in chromosomes of phytohemagglutinin-stimulated lymphocytes from 12 patients with laryngeal carcinoma and 12 healthy subjects were studied using the gelatine silver staining technique. This study was undertaken to examine whether any disease associated changes occur in NOR activity. A lower mean number of Ag-NORs per metaphase (t test, 0.05 > p > 0.02) was found in patients compared to controls. This difference was not due to any specific group of acrocentric chromosomes (D or G). The mean number of NOR associations per metaphase was also found to be markedly lower (t test, 0.01 > p > 0.001) in patients than in controls. This difference was principally due to the significant decrease in the associations between 2 chromosomes (t test, 0.02 > p > 0.01), and in particular to the decrease in the D-G type associations (t test, 0.05 > p > 0.02). These findings are discussed in relation to existing data on the nucleolar activity of lymphocytes in a variety of solid tumours and leukemias.