A study was conducted to determine the importance of algae as sources of orgnanic precursors in the haloform reaction. Two species each of green and blue-green algae were grown in laboratory conditions and harvested periodically during their growth cycle. The principal part of the study was directed toward determining the patterns of extracellular products excretion into the medium and of the chloroform produced after chlorination. Similar studies of cell suspensions were conducted. The study also included an analysis of the chloroform yields from chlorinated reservoir sediments and pure compounds known to be algal extracellular metabolites. The results indicated that the extracellular products of growing algal cells have the greatest potential as haloform precursors and that the greatest excretion of high chloroform-yielding compounds generally occurred during exponential growth. The blue-green algae were found to liberate more organic carbon than the green algae and produced higher chloroform concentrations upon chlorination. However, the green algae generally showed excretion of higher chloroform-yield compounds. The chloroform yields per unit organic carbon for the algal extracellular products often exceeded those reported for the humic substances and, therefore, could be considered of equal or greater importance as haloform precursors under certain conditions. Yields from solutions of pure compounds and from the sediments were significantly lower than those from the extracellular products and biomass of growing algal cells. Increasing the pH of the solutions of pure compounds resulted in higher chloroform yields, a result that has been demonstrated by others. / Master of Science