An overall practical dosimetric study of a 10-MV photon beam produced by a Varian Clinac-18 linear accelerator is presented. In particular measurements were made to provide data which could be utilized in computerized dosage calculations using the concept of dividing the radiation beam into primary and scatter components. From the measured percentage depth doses, tissue-phantom ratios are calculated. Special consideration is given to the derivation and mesurement of zero-area tissue-phantom ratios such that scatter-phantom ratios could be obtained. The computer techniques were tested under a number of specified conditions by comparing the calculated results to the measured data. The variation of dose with field size and distance is considered and attenuation data for shielding, wedge and compensating materials is provided.