AIM To explore the molecular spectra and mechanism ofhuman hypoxanthine guanine phosphoribosyl transferase(hprt)gene mutation induced by ethyluitrosourea(ENU)and~(60)Co γ-rays.METHODS:Independent human promyelocytic leukemiacells(HL-60)mutants at the hprt locus were isolated fromuntreated,ethyluitrosourea(ENU)and ~(60)Co γ-ray-exposedcells,respectively,and verified by two-way screening.Thegenetic changes underlying the mutation were determinedby multiplex polymerase chain reaction(PCR)amplificationand electrophoresis technique.RESULTS:With dosage increased,survival rate of platedcell reduced(in the group with dosage of ENU with 100-200μ/ml,P<0.01;in the group with dosage of ~(60)Co γ-ray with2-4 Gy,P<0.05)and mutational frequency increased(inthe group of ENU 12.5-200.0 μg/ml,P<0.05;in the groupof ~(60)Co γ-ray with 1-4 Gy,P<0.05)significantly.In the 13spontaneous mutants analyzed,92.3 % of mutant clonesdid not show any change in number or size of exon,a singleexon was lost in 7.7 %,and no evidence indicated total genedeletion occurred in nine hprt exons.However,deletions werefound in 79.7 % of ENU-induced mutations(62.5-89.4 %,P<0.01)and in 61.7 % of gamma-ray-induced mutations(28.6-76.5 %,P<0.01).There were deletion mutations in all9 exons of hprt gene and the most of induced mutationswere chain deletion with multiplex exons(97.9 % in gamma-ray-induced mutants,88.1% in ENU-induced mutants).CONCLUSION:The spectra of spontaneous mutationsdiffers completely from that induced by EUN or ~(60)Co γ-ray.Although both ENU and γ-ray can cause destruction ofgenetic structure,mechanism of mutagenesis between themmay be different. AIM To explore the molecular spectra and mechanism of human hypoxanthine guanine phosphoribosyl transferase (hprt) gene mutation induced by ethyluitrosourea (ENU) and ~ (60) Co γ-rays. METHODS: Independent human promyelocytic leukemia cells (HL-60) mutants at the hprt locus were isolated from untreated, ethyluitrosourea (ENU) and ~ (60) Co γ-ray-exposed cells, respectively, and verified by two-way screening. These genetic changes underlying the determined mutations were determined by multiplex polymerase chain reaction (PCR) amplification and electrophoresis techniques. With dosage increased, survival rate of plated cells reduced (in the group with dosage of ENU with 100-200 μ / ml, P <0.01; in the group with dosage of ~ (60) Co γ-ray with 2-4 Gy, P <0.05 ) and mutational frequency increased (inthe group of ENU 12.5-200.0 μg / ml, P <0.05; in the group of 60Co γ-ray with 1-4 Gy, P <0.05) significantly.In the 13spontaneous mutants analyzed, 92.3% of mutant clonesdid not show any change in number or size of exon, a singleexon was lost in 7.7 %, and no evidence indicated total genedeletion occurred in nine hprt exons. Yet, deletions were found in 79.7% of ENU-induced mutations (62.5-89.4%, P <0.01) and in 61.7% of gamma- 76.5%, P <0.01) .There were deletion mutations in all9 exons of hprt gene and the most of induced mutations chain deletion with multiplex exons (97.9% in gamma-ray-induced mutants, 88.1% in ENU- induced mutants) : The spectra of spontaneous mutations differents completely from that induced by EUN or ~ (60) Co γ-ray. Although both ENU and γ-ray can cause destruction of genetic structure, mechanism of mutagenesis between themmay be different.