Remission induction and continuation therapy in children with their first relapse of acute lymphoid leukemia. A Pediatric Oncology Group study. Between January 1979 and April 1983, 113 children undergoing their first relapse of acute lymphoid leukemia (ALL) at any site were registered in Pediatric Oncology Group study 7834; 98 were eligible and evaluable. In addition to radiotherapy administered to sites of local relapse, induction consisted of vincristine, doxorubicin, and prednisone (VAP) chemotherapy. Continuation therapy consisted of triple-drug intrathecal therapy and regimens of 6-thioguanine and cytarabine alternating with vincristine, prednisone, cyclophosphamide, and cytarabine. Randomization in continuation was between VAP pulses or no pulse, regardless of the site of relapse. This report provides long-term follow-up of these patients. Thirty-two of 39 children with bone marrow involvement achieved a complete response (CR). Only one of these is alive in an unmaintained remission, a child who did not have an initial CR. Thirty-four of 36 evaluable children with central nervous system involvement as the site of relapse achieved CR. Of these ten are alive; eight are in continuing CR. Nineteen of 20 boys with testicular relapse achieved CR. Of these, 14 are still alive and not receiving therapy, although only one half received treatment in compliance with the protocol described. These results illustrate the possibility of cure of patients who have relapsed with ALL when it is (1) confined to a meningeal or gonadal site and (2) treated vigorously with radiotherapy and a new regimen of systemic chemotherapy. The results reconfirm the need to prevent an initial relapse at any site. 