The prime-focus photoelectric spectrum scanner and a small telescope 4 inches in diameter have been used to make spectrophotometric comparisons between the primary standard star, a Lyr, and several radiation sources to determine the absolute spectral energy distribution of a Lyr from 3300 to 10800 A. The radiation sources were (1) a tungsten ribbon-filament lamp accurately calibrated at the U.S. National Bureau of Standards, (2) a blackbody cavity operated at the melting point of copper, and (3) a blackbody cavity operated at the melting point of platinum. The spectral energy distribution of a Lyr is shown in a figure and given in a table. The absolute flux from a star of apparent visual magnitude V = 0.00 at 5480 A is found to be 3.65 X 10-20 erg Hz-i or 3.64 X 10- erg A-i. The accuracy of this figure is estimated to be 2 percent.