From November 1977 to July 1983, 82 children with T leukaemia/lymphoma entered a randomised trial of combination chemotherapy and radiotherapy. Twenty-five were designated T lymphoma and 57 T leukaemia, 28 having greater than 100 x 10(9)1(-1) blasts in peripheral blood at diagnosis. Twenty-seven patients with mediastinal primaries who were treated on the companion non-Hodgkin lymphoma (NHL) trial were comparable in all respects to the T lymphoma patients and the results of treatment were therefore combined and analysed together. Overall 4-year survival (48-53%) and failure-free survival (FFS) (37-40%) were similar in all groups except the 28 with T leukaemia and WCC greater than 100 X 10(9)1(-1) (20% and 13%). There was a significant advantage in FFS for patients randomised to receive low dose mediastinal radiation, and this was most marked in patients with T lymphoma (66% vs 18%, P = 0.006).