目的　探讨 5 氨基酮戊酸光动力学疗法 (ALA PDT)体外伤杀肿瘤细胞的最佳照光时机和最佳照光能量。方法　用ALA诱导人喉癌细胞株HEP 2产生内源性的原卟啉Ⅸ ,以功率密度为 30mW/cm2 的He Ne激光 ,分别照射与ALA共同培养 1、4、8、12、48h的HEP 2细胞 ,并对与ALA共同培养 8h的HEP 2细胞 ,以同样功率密度的He Ne激光 ,分别照射 0 5、1 0、2 0、3 0、4 0min ,能量密度分别为 0 9、1 8、3 6、7 2、14 4J/cm2 。用MTT法测定照光后HEP 2细胞的死亡率。结果　 (1)光照时机选择在ALA与HEP 2细胞培养 8h时杀伤效应最强 ;(2 )ALA PDT对HEP 2细胞的杀伤效应与照光能量呈正相关 (r=0 88,P <0 0 5 )。结论　ALA PDT能有效地杀伤体外培养的肿瘤细胞 ,其杀伤最佳效果与照光时机和照光能量有关。 Objective To investigate the optimal illumination timing and optimal illumination energy of 5 ALA PDT to kill tumor cells in vitro. Methods Endogenous protoporphyrin IX was induced by ALA in HEP ​​2 cells and irradiated with He Ne laser at a power density of 30 mW / cm 2 for 1, 4, 8, 12 and 48 h, respectively 2 cells were irradiated with HEP 2 cells co-cultured with ALA for 8 h. The He Ne laser with the same power density was irradiated for 0 5, 1 0, 2 0, 0 0, 0 0, and 0 0 for 0 h, respectively. The energy densities were 0 9, 1 8 , 3 6,7 2,14 4J / cm2. The death rate of HEP 2 cells was measured by MTT assay. Results (1) The killing effect was the strongest when ALA and HEP 2 cells cultured for 8h. (2) The killing effect of ALA PDT on HEP ​​2 cells was positively correlated with the light energy (r = 0 88, P 0 05) . Conclusion ALA PDT can effectively kill tumor cells cultured in vitro. The best killing effect of ALA PDT is related to light timing and light energy.