A comprehensive data linkage system for the detailed investigation of occupational cancer has newly been established in the Danish Cancer Registry, providing employment histories back until 1964. Based on this system a study of 839 cases of cancer of the nasal cavities, sinuses and rhinopharnyx and 2,465 cancer controls diagnosed in Denmark during the period 1970-1982 was conducted. Histories of exposure to formaldehyde, wood-dust and 10 other specified compounds or procedures, were assessed by industrial hygienists unaware of the case-control status of the cancer patients under study. Some 4.2% of the male and 0.1% of the female controls had been exposed to formaldehyde. A statistically significant excess risk (p less than 0.05) for carcinoma of the nasal cavity and sinuses among males with a history of exposure to formaldehyde (RR = 2.8), wood-dust (RR = 2.5) and paint lacquer and glue (RR = 2.1) was found. When adjustment was made for wood-dust exposure the relative risk associated with formaldehyde was reduced to 1.6, which is not significantly in excess of 1.0, although still compatible with a 3- to 4-fold increase in risk using conventional 95% confidence limits. The joint action of exposure to wood-dust and formaldehyde was in accordance with an additive effect. The excess risk of sino-nasal cancer with exposure to paint, lacquer and glue remained statistically elevated after adjustment for contemporary exposure to wood-dust and formaldehyde.