There is a renewed interest in the application of photoconductors especially amorphous selenium (a-Se) to x-ray imaging. A new method for evaluating W +/-, the energy absorption necessary to release an electron-hole pair in a-Se is described. All previous methods used for the evaluation of the x-ray sensitivity of a-Se measure a change in surface potential on a charged plate due to irradiation by x rays. This results in a measurement of W +/- and other factors in combination. These factors include the energy absorbed from the spectrum of irradiating x rays and the a-Se layer capacitance. Such indirect methods are prone to error. A direct method for the evaluation of W +/-, which is based on the pulse height spectra resulting from the absorption of individual monoenergetic x-ray photons in a-Se, has been developed.