This case-control study of nasal and paranasal sinus tumors, in males diagnosed between 1978 and 1981 in the Netherlands, was designed to identify environmental risk factors. Special attention was given to assessing any association between nasal cancer and an occupational history of possible formaldehyde exposure while taking into account histologic type of tumor, history of tobacco use, and occupational exposure to wood dust. Of the 116 cases and 259 controls identified, interviews were completed for 91 (78%) of the cases and 195 (75%) of the controls. Adenocarcinoma was strongly associated with a history of high wood dust exposure (RR = 27.0). Two independent assessments of the association between possible formaldehyde exposure and the risk for nasal cancer were carried out (Assessments A and B). By Assessment A the relative risk for nasal cancer associated with possible formaldehyde exposure was 2.5 and by Assessment B it was 1.9. The risk appeared to be most strongly associated with squamous-cell carcinoma and could not be attributed to differences between cases and controls in age, smoking habits, or wood dust exposure. By its retrospective nature, the classification of formaldehyde exposure in this study is not based on known exposures to formaldehyde but on assessment of employment in jobs where formaldehyde exposure is thought possible. Given the limitations of the study, the authors do not consider that it provides conclusive evidence of a carcinogenic effect for formaldehyde, but that it indicates a need for further research--particularly into formaldehyde and squamous carcinoma of the nose.