Alveolar air samples were collected from 163 subjects at indoor swimming pools and from 77 nonexposed subjects. Chloroform was present in all samples collected from exposed subjects (median = 695.02 nmol/m3). It was found at very low levels in 53% of samples from nonexposed subjects. Alveolar air chloroform levels from people attending indoor swimming pools (mean value within each sampling session) were correlated with environmental air concentration (r = 0.907, p = .002). Analysis of variance showed that levels of chloroform in alveolar air depend on environmental air concentration, age, intensity of the sport activity, and kind of swimming. Chloroform levels in samples collected from competitive swimmers versus nonswimming visitors were different (F = 10.911, p = .001). Moreover, their pattern of swimming may affect chloroform concentration in alveolar air. The analysis of chloroform in alveolar air assesses indoor exposure in healthy subjects simply and at low cost.