Standard solutions of phosphorus‐32 and iodine‐131 are now included among the radioactive standards distributed or calibrated by the National Bureau of Standards for the benefit of investigators in physics, chemistry, medicine, and industry. These particular isotopes have been employed extensively for diagnosis and therapy in brain surgery, leukemia and other types of cancer, and in their early use, variations in the results obtained by different laboratories are said to have amounted to as much as 200 percent of the accepted value. The Bureau's new procedure for making the standard samples available to research workers will now permit the duplication of results at different laboratories.