BACKGROUND: The overall prognosis of acute leukemia has dramatically improved in the past 20 years, primarily due to the use of intensive multiagent chemotherapy in combination with CNS prophylaxis. However, increased aggressiveness of treatment protocols was entailed a great risk of various toxic effects. Endocrine function was also affected. The aim of this study is to compare the effect of chemotherapy on thyroid function in children with acute leukemia. METHOD: Parameters of thyroid function during chemotherapy were measured in 11 children with acute leukemia. Level of the serum 73,74 and TSH were determined before therapy, 7th day and 30th day of chemotherapy. Determination of serum 73, 74 and TSH were performed by conventional radioimmunoassay technique. Statistical analysis was done using SAS software. RESULT: 1) Level of level 73 was normal in 7 cases before therapy and decreased in 9 cases on 7th day of remission induction therapy. On 30th day, 73 level was increased to normal value. 2) Level of 74 was normal before therapy and decreased on 7th day of therapy. On 30th day of therapy 74 level showed various change. Three of them showed sustained low level of 74 on 7th and 30th day. 3) Level of TSH were normal before therapy and decreased on 7th day of therapy, followed achievement of normal level after completion of induction therapy. CONCLUSION: We conclude that during induction chemotherapy in childhood acute leukemia, thyroid function was impaired which was reversible.