The formation of five volatile disinfection by-products (DBPs: chloroform, bromodichloromethane, chloral hydrate, dichloroacetonitrile, and 1,1,1-trichloropropanone) by the chlorination of the materials of human origin (MHOs: hair, lotion, saliva, skin, and urine) in a swimming pool model system was examined. Chlorination reactions took place with a sufficient supply of chlorine residuals (0.84 mg Cl2/l < total chlorine < 6.0 mg Cl2/l) in 300 ml glass bottles containing either ground water or surface water as a reaction medium at 30 degrees C and pH 7.0, for either 24 or 72 h. A longer reaction period of 72 h or a higher content of organic materials led to the increased formation of DBPs. Of the DBPs formed by the reaction, chloroform was a major compound found in both ground and surface waters. The formation of chloroform and bromodichloromethane per unit total organic carbon (TOC) concentration was suppressed when all types of MHOs were added to the surface water that already contained DBP precursors such as humic substances. However, the formation of dichloroacetonitrile was promoted, probably due to the increased degradation reactions of nitrogen-containing compounds such as urea and proteins of human origin. In conclusion, the materials of swimmers' origin including hair, lotion, saliva, skin, and urine add to the levels of DBPs in swimming pool water, and any mitigation measures such as periodic change of water are needed to protect swimmers from elevated exposures to these compounds.