In this article, exposure to trihalomethanes (THMs) in indoor swimming pools as a consequence of water chlorination is reported. Environmental and biological monitoring of THMs was performed in order to assess the uptake of these substances after a defined period in five competitive swimmers, regularly attending an indoor swimming pool to train for competition during four sampling sessions. Analyses were performed by gas-chromatography and the following THMs were detected: chloroform (CHC13), bromodichloromethane (CHBrC12), dibromochloromethane (CHBrsC1) and bromoform (CHBr3). CHC13 appeared the most represented compound both in water and in environmental air before and after swimming. CHBrC1w and CHBr2C1 were always present, even though at lower levels than CHC13, CHBr3, was rarely present. In relation to biological monitoring, CHC13, CHBrC12 and CHBr2C1 were detected in all alveolar air samples collected inside the swimming pool. Before swimming, after 1 h at rest at the pool edge, the mean values were 29.4 +/- 13.3, 2.7 +/- 1.2 and 0.8 +/- 0.8 micrograms/m3, respectively, while after spending 1 h swimming, higher levels were detected (75.6 +/- 18.6, 6.5 +/- 1.3 and 1.4 +/- 0.9 micrograms/m3, respectively). Only CHC13 was detected in all plasma samples (mean: 1.4 +/- 0.5 micrograms/1) while CHBrC1x and CHBr2C1 were observed only in few samples at a detection limit of 0.1 micrograms/1. After 1 h at rest, at an average environmental exposure of approx. 100 micrograms/m3, the THM uptake was approx. 30 micrograms/h (26 micrograms/h for CHC1c, 3 micrograms/h for CHBrC12 and 1.5 micrograms/h for CHBr2C1). After 1 h swimming, the THM uptake is approx. seven times higher than at rest: a THM mean uptake of 221 micrograms/h (177 micrograms/h, 26 micrograms/h and 18 micrograms/h for CHC13, CHBrC12 and CHBr2C1, respectively) was evaluated at an environmental concentration of approx. 200 micrograms/m3.