Indoor and outdoor formaldehyde and acetaldehyde levels were assessed to characterize pollution in dwellings in the city and the Province of Bari, also taking into account seasonal variability, and to investigate health effects of aldehyde exposure on the general population. In 2007, passive environmental monitoring was performed, for 24 hours, in the kitchen of 59 dwellings, as well as outdoors for 27 of them. A questionnaire probing personal and home characteristics was administered to all 182 subjects habitually resident in the homes. During the period January-June 2008, formaldehyde and acetaldehyde levels were monitored monthly in 20 of the investigated dwellings inhabited only by non smokers. Indoor formaldehyde and acetaldehyde concentrations were significantly higher (16.0 +/- 8.0 and 10.7 +/- 8.8 microg m(-3)) than outdoor concentrations (4.4 +/- 1.7 and 3.4 +/- 2.0 microg m(-3)), showing a correlation between indoor levels of the two aldehydes (r = 0.41; p = 0.001). In dwellings inhabited only by non smokers, formaldehyde concentrations were higher in the presence of furniture bought new or restored less than one year before (p = 0.03). Formaldehyde and acetaldehyde levels were significantly higher in winter months than in spring-summer months (F = 2.86, p = 0.02; F = 5.39, p < 0.001) and seemed to be influenced by the time that kitchen windows were kept open. As regards the effects on human health, a low prevalence of allergic disease and no association between any irritant or allergic complaints and indoor levels of the two aldehydes was observed. In conclusion, the results showed low indoor and outdoor concentrations of formaldehyde and acetaldehyde, not generally posing a risk for human health.