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We observed the radio spectrum of two gravitationally lensed sources, MG 0414+0534 and PKS 1830-211, to search for neutral hydrogen absorption associated with the foreground lensing galaxies. The primary purpose of these observations is to determine the redshift of the lensing galaxies, which are both extremely faint, making optical determinations difficult at best. The observations were performed on the Greenbank 140$'$ telescope using the spectral processor. The observed frequency range extends from 750 to 1000 MHz, corresponding to a redshift range of 0.42 $\le$ z $\le$ 0.9, and covers most of the range in redshifts predicted by lensing models. The main difficulty with observations in this frequency range is severe interference from a variety of sources. We discuss several methods of minimizing the effects of such interference and present our results in terms of optical depth limits as a function of wavelength.
