The effect of beta‐radiation from C14has been examined on nineteen different films. The method employed uses a ``radiator,'' a set of eight radiating sources of different intensities, to replace the stable light source and absorbing wedge common in spectral photometry. With this device sensitivity and contrast of the nineteen films have been measured. Based upon these results and a microscopic estimation of grain size, recommendations are made for the most desirable film for use in radioautography and detection of radioactivity. Of the films examined, Eastman No‐Screen x‐ray film appears best for the detection of the beta‐rays, and Ansco Reprolith, and Eastman Type M x‐ray stripping films appear to be most desirable for work with radioautographs.