Biological radioisotope studies suffer from a lack of sensitive measurement techniques and therefore traditionally require large amounts of labeled material to produce a measurable signal. Such quantities of materials are often significantly higher than naturally-occurring levels preventing these studies from replicating physiological conditions. AMS affords the sensitivity necessary to perform biological radioisotope studies with low levels of labeled material that preserve physiological conditions. The choice of labeled material can substantially affect the ease of interpretation and comprehensiveness of these studies. Here, the benefits and limitations of whole-cell labeling with (14)C-glucose and targeted pathway labeling with (14)C-nicotinic acid are discussed and compared.