The first of four volumes in Research Report No. 7 of the Health Services Mobility Study (HSMS), this book contains 143 task descriptions covering most of the medical activities carried out by diagnostic radiologists. (The work carried out by radiologic technologists, and administrative, machine-related, and nursing-type functions are found in Volumes 2 and 3. Volume 4 is an index of all the tasks in the three volumes.) The first three volumes present the tasks in a given area in numerical order by code number. These task descriptions are offered for use as instructional materials, as inputs to the design of career ladders, for the structuring of jobs and assignment of work to job titles, and as inputs to the development of performance evaluation instruments and proficiency tests. Chapter I of this volume defines "task" and tells how the descriptions were developed. The task descriptions are presented in Chapter 3 by Code Number, the steps of the task described in logical sequence in considerable detail. Chapter 2 is a guide to the tasks, arranged in logical grouping for easy reference: (1) By system of the body, (2) by function (e.g., consultations, procedures, teaching), and (3) by main type of recipient (e.g., patient, pediatric patient, student, etc.). (HD)