The study of gonadal exposure dose from diagnostic x-ray procedures to be reported here was undertaken (a) to provide the clinicians at the University of Colorado Medical Center with information about such exposures when a given examination is ordered, and (b) to add to the body of information on this subject. Until relatively recently, the question of radiation dose to the gonads has been neglected in favor of air dose at the skin or skin dose. Stanford and Vance (1), Ardran and Crooks (2), Billings, Norman, and Greenfield (3), and Webster and Merrill (4), among others, have recently published data on gonadal dose. Already a large range of variation in the doses obtained with different installations during the performance of the same x-ray examinations is apparent. For the present study three approaches were used: measurements in patients during actual examinations, measurements in phantoms, and measurements in cadavers. The technics of measurement and the difficulties involved will be discussed subsequently. General Considerations There are two basic situations: In one the gonad is in the useful x-ray beam; in the other the gonad is outside the useful beam. In the first situation, the dose is due to the primary radiation plus scattered radiation and can be calculated from the known exposure dose in air at the body surface distance and from a depth-dose chart appropriate to the factors used. Such a series of charts has been published by Trout, Kelley, and Cathey (5). In the second situation, the dose is due almost entirely to scattered radiation (sometimes called “internal scatter”), and the solution is essentially the same, except that dose information for points outside the useful beam is not readily available. An example of such information is shown in Figure 1. If the same factors with which these data were obtained are used for examination of a female, the gonadal dose can be estimated by multiplying the milliroentgens per milliampere-second (mas) for the estimated distance from the central ray to the ovaries by the mas actually used. For examinations where the gonads are outside the useful beam, direct measurement during actual examination is often impractical because of the relative insensitivity of available instruments. We were able, however, to estimate male gonadal dose during photoroentgen chest examinations by placing a pocket dosemeter in the groins of a series of patients and dividing the accumulated reading by the number of patients to obtain an average. This method is impractical for obtaining female gonadal dose because of the inaccessible location of the ovaries. Physical Factors The principal physical factors influencing the gonadal dose are as follows: