Sixty-eight previously untreated patients with IgG myeloma who were entered into five protocols of Cancer and Leukemia Group B (CALGB) were studied in order to determine the possible influence of excretion of kappa versus lambda urinary light chains on responses to treatment and survival. All patients in these protocols were included if the serum and urine protein abnormalities were confirmed by one of the two group reference laboratories. Pretreatment characteristics of the two groups of patients did not differ significantly. Of 44 patients with kappa Bence Jones proteinuria, 19 patients (43%) had good responses to treatment, whereas only 3 of 24 patients (13%) with lambda Bence Jones proteinuria had good responses (p = 0.02). Survival for the patients excreting kappa light chains was significantly better than survival for patients excreting lambda chains (median survival 31 versus 12 mo, p = 0.02).