Brominated trihalomethanes are volatile organic liquids that have a number of industrial and chemical uses. The chief reason for health concern is that they are generated as by-products during the disinfection of drinking water. The brominated trihalomethanes occurring in water are bromoform, dibromochloromethane, and bromodichloromethane. These compounds are formed when hypochlorous acid oxidizes bromide ion present in water to form hypobromous acid, which subsequently reacts with organic material to form the brominated trihalomethanes. Section 1412 (b) (3) (A) of the Safe Drinking Water Act, as amended in 1986, requires the Administrator of the Environmental Protection Agency to publish Maximum Contaminant Level Goals (MCLGs) and promulgate National Primary Drinking Water Regulations for each contaminant, which, in the judgment of the Administrator, may have an adverse effect on public health and which is known or anticipated to occur in public water systems. This document provides the health effects basis to be considered in establishing the MCLGs for brominated trihalomethanes found in chlorinated drinking water. To achieve this objective, data on pharmacokinetics, human exposure, acute and chronic toxicity to animals and humans, epidemiology and mechanisms of toxicity were evaluated. Specific emphasis is placed on literature data providing dose-response information.