To investigate the mechanism of biological effects induced by low dose radiation, the alterations of transcriptional profiles of human normal lymphoblastoid cell AHH-1 lines irradiated with different doses of ?-rays were assayed. AHH-1 lines were irradiated with ?-rays of 0.1, 0.5, and 1.0 Gy, respectively, with the unirradiated cells as control group. Total RNA of irradiated cells was extracted 4 h after irradiation, and then cDNA microarray was used to detect the transcriptional profiles of the cells. The different expressions of genes were assayed by hierarchical cluster analysis, gene ontology and pathway analysis, and then identified by real-time Q-PCR. The results of real-time Q-PCR of CASP9 were in accordance with microarray assays. The microarray assays showed that there were 1 330 up-regulated genes and 1 002 down-regulated genes in three irradiated groups. Alterations of 18 genes expression were related with absorbed dose. Among these genes, 16 genes were positive relation, and 2 genes were negative relation with dose. The results of hierarchial cluster analysis indicated that the similarity of the expression profiles of 0.1 Gy and 1.0 Gy was the highest among 4 groups. These altered genes could be related to multiple signal transductions, such as cell cycle, p53 signal pathway, base excision repair, RNA transport, endoplasmic reticulum proteins processing pathways, and so on. These differential expressed genes detected by cDNA microarray would help to elucidate the mechanisms of biological effects of low dose irradiation. New biological dosimeter for low dose exposure might be developed from these dose-related genes.Cited