Experimental procedures have been carried out to determine the feasibility of the substitution of radioactive nuclides or isotopes for conventional x-ray machines in the production of radiograms or roentgenograms. Radio active nuclides with proper characteristics can be fabricated into a very small portable source. Of approximately 1,300 currently known radioactive nuclides, only 48 appeared to have properties suitable for this purpose and to be worthy of detailed study. The present study indicated that only 11 of these met the criteria essential for eventual clinical usefulness. The criteria chosen were that the radioactive nuclides should 1 be readily available, 2 be capable of easy production, 3 have a half-life of one month or more, 4 possess a suitable emission spectrum, and 5 be capable of providing a high specific activity source. Some of the important properties of the 48 radioactive nuclides, used in their evaluation in accordance with the five criteria, are listed. Although no one nuclide holds first position in each of the above five criteria, nevertheless I125, Cs131, Ce144, Sm145, Gd153, Eu155, Dy159, Yb169, Tm170, Hf175, and W181 reasonably satisfy the requirements for isotopic radiography.