Forty-six patients with acute lymphoblastic leukemia (ALL) in first marrow remission underwent allogeneic marrow transplantation between August 1976 and June 1985. Thirty-four patients had no extramedullary disease after remission induction and 12 had extramedullary relapses prior to or at the time of marrow grafting. The conditioning regimen included cyclophosphamide followed by total body irradiation, 9.2-15.75 Gy, administered as a single dose or in six or seven daily fractions. Marrow donors were genotypically HLA-identical siblings. Methotrexate was given as prophylaxis for graft-versus-host disease (GVHD). Forty-four patients had marrow engraftment. The incidence of grades II-IV acute GVHD was 52%. Clinical chronic GVHD occurred in 21 patients. Eighteen patients are alive 1-9 years (median = 4.2 years) after marrow grafting, 15 of whom are in continuous complete remission. The estimated probability of relapse within 2 years (+/- standard error) is 41 +/- 9% and the probability of relapse-free survival at 5 years is 28 +/- 7%. Major causes of death were recurrent leukemia, acute GVHD and interstitial pneumonia. Actuarial probabilities of survival, relapse and disease-free survival were not significantly different between those patients who did and those who did not have extramedullary disease after attaining first marrow remission.