We investigated the relationship between visual field defects and some clinical factors in 30 eyes of 30 normal-tension glaucoma (NTG) patients. The static central visual field by the Humphrey field analyzer, diurnal variation of intraocular pressure (diurnal IOP), blood flow velocity of the ophthalmic artery by color Doppler imaging, blood flow volume of digital tissue by laser flowmetry, and systemic blood pressure (BP) were measured after rinsing out the anti-glaucoma drug for one month. Mean deviation (MD) calculated by the Humphrey STATPAC program as an index of visual field defect, was correlated to the Pourcelot index (RI) of ophthalmic arterial blood flow and magnitude of diurnal IOP. In multiple regression analysis, the multiple correlation coefficient was 0.79 and the coefficient of determination was 0.62. RI, systolic BP, magnitude of diurnal IOP, and the refraction and mean of diurnal IOP were used in the multiple correlation model as factors significantly related to MD. These results suggest that both IOP and some clinical factors may contribute to the visual field defects of NTG.