In 1973, R. B. Moon and J. H. Richards utilized phosphorus-31 nuclear magnetic resonance (('31)P-NMR) to examine the human erythrocyte and monitor its intracellular pH (Moon and Richards, 1973). Ever since this classic report, the field of in vivo NMR has virtually exploded. The growth of this technique can be attributed to its non-invasive nature and its ability to yield complete, real-time, metabolic profiles at a relatively low cost. In these two respects, nuclear magnetic resonance remains unchallenged by other physical techniques.;In this dissertation, ('31)P-NMR spectroscopy was applied to the study of (1) sipunculan erythrocytes (part 1), (2) spermatozoa isolated from several vertebrate and invertebrate species (parts 3-5), and (3) unfertilized eggs isolated from the blue crab and the horseshoe crab (part 6). Part 2 deals with the determination of P(,50) values for the oxygen-hemerythrin interaction in the presence or absence of effectors. This study was performed utilizing uv-visible spectroscopy.;('31)P-NMR results (parts 1, 3-6) center on the identification of key metabolites and on the determination of intracellular pH. In studies involving fish spermatozoa, emphasis was also placed on examining changes in metabolic profiles following (1) an anaerobic insult, (2) motility initiation, or (3) short-term storage. This dissertation also captures several difficulties in spectral interpretation which a spectroscopist is likely to encounter.