Annual report of the Argonne National Laboratory Radiological and Environmental Research Division regarding activities related to the Center for Human Radiobiology. The papers in this report deal with several different aspects of the Center's studies of the effects of internally deposited radionuclides in humans: experimental and theoretical research on the induction of tumors by alphaparticle irradiation (papers 1-4); medical effects (papers 5-8); metabolism and dosimetry (papers 9-17); methods for the detr-mination of radioactivity (papers 18-25); and processing of data (papers 26-27).