The most commonly received complaints and comments about water quality from ground water in central Missouri are in regard to the unpleasant taste and odor resulting from the presence of dissolved iron and hydrogen sulfide. The purpose of the investigation was to determine the relative importance of source rock mineralogy and the kinds and abundances of microorganisms in ground water in controlling the iron and sulfide concentrations in ground water. The subsurface water samples studied were out of redox equilibrium with respect to dissolved nitrogen gas. The relationships between nitrate, nitrite, and ammonia in these samples are not consistent with any equilibrium or metastable equilibrium model which can be developed from current thermodynamic data. It is most likely that either the water samples are not in any kind of equilibrium configuration with respect to nitrite or that the free energy data for nitrite are in error. (Author)