This study involved an assessment of chloroform formation due to the use of hypochlorite-containing detergents in dishwashers. The objective of this research was to quantify in-home formation of trihalomethanes, particularly as related to dishwasher usage. A series of 14 flask and 15 laboratory experiments were completed. Flask experiments involved the mixing of food with dishwasher detergent in water for a 12-min reaction period, and were intended to identify chemicals and relative levels of those chemicals that may form from dishwasher usage with different food groups. Liquid concentrations of chloroform ranged from 1 to 41 mg/l. Laboratory experiments involved collection of liquid and gas samples over the course of an operating cycle with an actual residential dishwasher. Background concentrations of chloroform in the water supply were generally between 0 and 10 microg/l; liquid chloroform levels in the wash cycle were typically at least 50 microg/l. Chloroform concentrations were as high as 20 microg/l in the dishwasher headspace. Using mass balance equations for a typical residential house and laboratory results from this research, predicted concentrations resulting from dishwasher usage were similar to typical background concentrations in residential dwellings.