In a case-control study of occupational and environmental causes of cryptogenic fibrosing alveolitis we recently observed a higher prevalence of self-reported symptoms of wheeze, rhinitis or conjunctivitis in cases than in controls. To determine objectively whether this was due to a higher prevalence of atopy amongst cases of CFA, we have measured skin sensitivity to common allergens (D. Pteronyssinus, grass pollen, and cat fur), eosinophil counts and total Immunoglobulin E (IgE) in venous blood in the 22 surviving CFA cases from that study who were willing to provide a blood sample, and in one matched control per case. At least one positive skin test was recorded in 13 cases and six controls, the matched odds of one or more positive test being significantly increased in cases by a ratio of 8.0 (95% confidence interval 1.01-64, P = 0.05). Geometric mean eosinophil counts and IgE levels were also increased amongst cases by factors of 1.6 (95% CI 0.96-2.6) and 1.9 (0.9-3.8) respectively, although these differences were not significant. Differences in skin sensitivity, eosinophil counts, and IgE levels all tended to be more obvious in the 13 case control pairs in which the case was not taking steroids or other immunosuppressive treatment. We conclude that cases of CFA showed increased skin sensitivity to common allergens, and had evidence of increased IgE and eosinophilia in peripheral blood. These findings suggest that atopy may be an important determinant of susceptibility to CFA.