In a large group of 74 patients irradiated with 2400 rad for acute lymphoblastic leukemia an unusually high frequency of complete GH deficiency was observed (40 %). Only 11 out of 46 prepubertal children had growth retardation and seven children received hGH treatment. On the contrary 11 other prepubertal cases had normal growth rates in spite of lack of response to AITT. Plasma SmC values were correlated with growth rates but were discrepant with GH responses to AITT in somecases. Because of this high frequency of GH dysregulation further growth at time of puberty should be carefully documented.