Abstract: 6-131 I-cholesterol was prepared by the isotope exchange method. Effects of temperature and carrier amounts on the percentage of labeling were examined and the optimum labeling conditions ascertained.Both 19-131 I-and 6-161 I-cholesterol were synthesized for the purpose of comparison, the latter was proved to be superior in several aspects such as ease of preparation, simplicity of labeling procedure, high yield, constant quality and easy storage. 6-131 I-cholesterol was subjected to clinical trials in several hospitals. Results of studies show that 6-131 I-cholesterol is also a good adrenal scanning agent.