From january 1982 to january 1986 we treated 23 pediatric patients who had non Hodgkin's lymphoma, with a new therapeutic protocol. This protocol is based on the LSA2 L2, modified during the induction phase with high-dose methotrexate and increasing of intrathecal therapy. Nineteen patients (83%) were in stages III and IV and the 47.4% were in stage IV. The distribution according to histology was: 10 Burkitt's undifferentiated lymphomas; 2 non-Burkitt's undifferentiated lymphomas; 5 lymphoblastic lymphomas convoluted-cells; 5 lymphoblastic lymphoma non-convoluted cells and 1 indeterminate lymphoma. The follow-up oscillated between 6 months and 4 years. The total survival rate is 82.6% with a 100% survival in stages I, II and III and 63.5% in stage IV. The survival according histology is 91.7% for undifferentiated lymphomas and 70% for lymphoblastic lymphomas; the actuarial survival rates in the two groups at 30 months are 87% and 55% respectively (p greater than 0.10). We concluded that adding high-dose methotrexate to the LSA2 L2 protocol improve the survival rate in undifferentiated lymphomas and in a less extent in lymphoblastic lymphomas, without significant toxicity. This new protocol is mainly indicated in undifferentiated and indeterminate non-Hodgkin's lymphomas.