Untreated non-leukemic (lymphocytes less than or equal to 4.0 X 10(9)/l) patients with non-Hodgkin lymphoma (NHL) of B cell type often show an excess of B cells in peripheral blood bearing the same light chain isotype as the lymph node tumor cells which may indicate a leukemic spread of the disease. The ratio between kappa- and lambda-bearing lymphocytes (normal range 1.0-3.3) was studied to evaluate the prognostic significance of clonal B cell excess (CBE) at diagnosis in 110 NHL patients. In total 43% had a CBE in peripheral blood. Fifty-two per cent of the patients in clinically advanced stages had CBE and 30% of the patients in stages I and II. CBE was detected in 49% of all patients with low-grade malignant lymphoma and in 32% with high-grade malignancy. Patients with a normal kappa:lambda ratio at diagnosis entered complete remission more often than those with CBE (P less than 0.01). In patients with high-grade but not with low-grade malignant lymphomas remission duration was longer for those with normal kappa:lambda distribution than for the patients with an abnormal ratio (P less than 0.01). Survival was not statistically significantly influenced.