SUMMARYThe transmission of optical radiation in the wavelength range 300–600 nm through thirteen human toenails obtained at autopsy was examined. The total transmitted radiation at fifteen different wavelengths was measured using an irradiation monochromator in conjunction with an integrating sphere and photodiode. A correction was included for fluorescence radiation from the nails.The nails exhibited decreasing transmission of optical radiation in the wavelength region 600–300 nm. These findings may be helpful in the understanding of photo‐onycholytic reactions and in the design of suitable regimens for the treatment of psoriatic nail ch