This booklet is one in a series of instructional aids designed for use by elementary and secondary school science teachers. The various units and forms of radioactive materials used by teachers are first considered. Then, the quantities of radioisotopes that a person may possess without a license from the Atomic Energy Commission (AEC) are discussed, including a list of radioisotopes and allowable quantities. Procedure for applying to the AEC for a license to possess greater quantities is reviewed. Safety guidelines for instructors and students are considered, including safety in dispensing radioisotopes in the laboratory, laboratory precautions, decontamination, storage of radioactive materials, and waste disposal. (PR)