Publisher Summary It is noted that there is a great need for improvement in classic procedures for quantitative microbiological determinations. In order to eliminate the growth period in a quantitative bacteriological determination, a method is required with a resolving power, at least, as great as that permitted by visible light, and a means for the rapid examination of a statistically significant portion of the unknown sample. Radioisotope techniques through their extreme sensitivity render extended incubation of organisms unnecessary and can meet the important requirement for speed. Another major requirement is accuracy, which can be significantly improved by using isotopes to explore biological vagaries and errors introduced through imperfect methodology. Radiation detection instruments can detect even a beta particle ejected from an atomic nucleus, which is like many trillions of times smaller than a bacterium. Continued exploitation of isotopes in microbiological research promises to elucidate many fundamental biochemical processes.