We report a novel measurement technique for the wide-band determination of the frequency response of photodetectors. It is based upon the accurate measurement of the photocurrent noise spectra under illumination with a light-emitting diode. The high sensitivity of −200 dBm/Hz within a frequency regime from 10 MHz to 1.6 GHz renders it particularly attractive for investigating the response behavior at low optical input levels and for characterizing frequency-dependent gain phenomena. The practical potential of the method is illustrated by applying it to various types of InGaAs-based photodetectors (p-i-n and avalanche photodiodes and metal-semiconductor-metal photodetectors).