The purpose of this study was to investigate the extent to which algal-produced organic matter may react with chlorine in aqueous solution to form trihalogenated methanes. Two species each of green and blue-green algae were cultured in an inorganic medium and harvested on several days throughout the growth cycle. Media filtrates and cell suspensions were analyzed for total organic carbon and chloroform produced after chlorination. Pure solutions of representative algal extracellular metabolites were analyzed in a similar manner. The highest-yielding (chloroform-carbon per total organic carbon) compounds were released during the late exponential growth phase. More organic carbon was accumulated in the external medium through the stationary growth phase by the blue-green species, but higher yields were obtained in the green algae cultures during these later stages of growth. The results indicate that the differences in the total chloroform production potential may be more significant among individual algal strains than between larger taxonomic divisions, such as the green and blue-green algae. None of the model compounds studied produced chloroform yields comparable to those of the. media filtrates or biomass. The chloroform-carbon yields of the culture filtrates were in the same range as those reported for the humic and fulvic acids, and in some cases much higher. Therefore, the algal extracellular products may be important as precursors in the formation of trihalomethanes during water treatment. / Master of Science