Twenty years ago the Public Health Service developed the first Radiological Health Handbook as a training aid, and it has since become a basic reference and a major resource for professional personnel and students in the field of radiological health. The present text includes information unavailable ten years ago: a new chart of the nuclides, a universal decay table in place of individual isotope listings, microwave and laser glossaries, film-speed charts, depth-dose tables, and a 'rules of thumb' section.