This paper reports the irritant effects associated with formaldehyde exposures in mobile homes. Week-long, integrated fomakldehy concentratioas were nm red uing paive monitors insummer and winter while the mobile home residents continued their normal activities. Information on acute health problems, chronic respiratory/allergic illnesses, smoking behavior, de v , and time spent at home was obtned on over 1000 individuals during the sampling period. Measured formaldehyde concentrations varied from under the limit ofdetection (0.01 ppm) to OA6 ppm. Formaldehyde exposure was estiated for each individual by multiplying the concentration measured in his or her home by the time he or she spent at home. Irritant effects were found to be associated with formaldehyde exposure after controlling for age, sex, smoking status, and chronic illnesses using a logistic procedure. Some of the interaction terms found to be significant indicated that there were synergistic effects between formaldehyde exposure and chronic health problems.