In the study of psychological effects of prolonged use of a respiratory protective device (RPD), forty 7-10-year-olds, fifty 12-15-year-olds and twenty-eight 17-20-year-olds participated as subjects. Subjects in the experimental groups wore a full-face mask provided for civil defence in Sweden, and subjects in the control groups wore a filtering facepiece consisting of a tissue material covering the nose and mouth. Subjects in both groups tended to terminate at the same time, implying that breathing resistance may not be an important obstacle to prolonged wear of the full-face mask. In the experimental groups 97% wore the mask for at least 1·5 h, 77% for at least 2·5 h and 54% for the full 6-h session. About 50% of subjects in the younger age groups terminated in the interval between 1·5 to 3·5 h, whereas the corresponding figure in the older age group was about 30%. Boredom may have played an important role for decisions to terminate, perhaps in part because the mask interfered with speech communication. Discomfort due to pressure on the nose, the chin and the forehead was also reported, more frequently by the older than by the younger subjects.