The formation of the latent image in photographic film by the absorption of radiation energy and the subsequent darkening of the film by chemical photographic processing for many years have provided a convenient system for the dosimetry of Xand y-radiation (1). By the suitable selection and combination of certain commercial X-ray film types and metal filters, exposure doses between 10-2 and 103 r are determined routinely within an accuracy limit of ?25 % over an effective energy range between 0.03 and 10 Mev. This paper contains the results of an investigation to determine the usefulness of these same commercial film types for measuring exposure doses higher than 103 r, by the films' darkening due to printout formation, without the need for photographic processing. At present, various chemical, glass, and solid-state systems are being employed in the dosimetry of very high doses of ionizing radiations, and the choice of a particular system is determined by the characteristics that suit the particular dosimetry problem. The graphite-sphere calorimeter (2), which is the proposed national standard instrument for the measurement of high-level dose (3), is not suited for routine dosimetry, required in food sterilization, for example. It has been suggested (3, 4) that, in order to span the range of 104 to 107 r encountered in food sterilization, the cobalt F-0621 glass dosimeter (4, 5) and the ceric sulfate chemical dosimeter (4, 6-8) be used in combination as a working standard dosimeter system, because they best satisfy the requirements of precision, exposure range, rate and energy independence, stability, convenience, etc., applicable to this field. In the case of the cobalt glass dosimeter, because of its inherent instability, the individual glasses need to be preirradiated to a certain density to give the desired precision at the lower portion of the useful range (104 to 105 r), and at the higher portion of the range (105 to 106 r) a correction for fading must be applied. The chief drawbacks in the use of the ceric sulfate dosimeter, whose range is normally 5 X 104 to 107 r,