A method for the estimation of the human intake of trihalomethanes (THMs), namely chloroform, bromodichloromethane, dibromochloromethane and bromoform, during showering and bathing is reported. The method is based on the determination of these compounds in exhaled breath that is collected by solid adsorption on Tenax using a device specifically designed for this purpose. Instrumental measurements were performed by automatic thermal desorption coupled to gas chromatography with electron capture detection. THMs in exhaled breath samples were determined during showering and swimming pool attendance. The levels of these compounds in indoor air and water were also determined as reference for interpretation of the exhaled breath results. The THM concentrations in exhaled breath of the volunteers measured before the exposure experiments showed a close correspondence with the THMs levels in indoor air where the sampler was located. Limits of detection in exhaled breath were dependent on THM analytes and experimental sites. They ranged between 170 and 710 ng m(-3) in the swimming pool studies and between 97 and 460 ng m(-3) in the showering studies. Application of this method to THMs determination during showering and swimming pool activities revealed statistically significant increases in THMs concentrations when comparing exhaled breath before and after exposure.