Chlorination of drinking water and wastewaters results in the formation of numerous compounds, including trihalomethanes (THMs). The THM formed most frequently during the chlorination of drinking water is chloroform. However, in coastal areas where wastewaters may be introduced into a marine environment, the relative concentration of brominated THMs increases dramatically. The toxicity of chloroform has been the most widely investigated of all the THMs, although the extent of its toxicological effects is not known. Most of this information has been determined for mammalian species. Experimental data on the toxicological effects of THMs on aquatic species are limited. The chapter presents data on the toxicity of THMs to isolated hepatocytes from striped bass (Morone saxatilis). This test system was chosen because the primary target organ in chloroform toxicity is the liver. Additionally, use of this in vitro system allows for greater control over the portion of the applied dose that actually reaches the target cells, and it is possible to measure more than one endpoint simultaneously.