With the extensive and expanding use of ultrasound in diagnostic medical procedures, significantly large numbers of the population are exposed to ultrasonic radiation. The developing fetus, in particular, is often subjected to a whole body insonation during the ultrasonic examination of the mother. Yet no definitive and critical studies have been performed to establish the safety of such procedures, particularly as far as dividing and differentiating cells are concerned. The research proposed aims to establish the toxic levels of ultrasonic energy which interfere with cell replication and its relation to diagnostic levels. It also seeks to determine whether sublethal damage is produced and if there is variation in radiation sensitivity within the cell cycle. BIBLIOGRAPHIC REFERENCES: Lele, P.P., Sofi J.W. & Svetz, P. (1975), "Studies on the Effects of Ultrasound on Cell Growth and Division", Proc. III New England Bioengng. Conf., Tufts Univ., 9-10 May, 1975. Sofia, J.W. & Lele, P.P. (1975), "Avian Egg as a Test System for Ultrasonic Teratological Studies", Proc. III New England Bioengng. Conf., Tufts Univ. 9-10 May, 1975.