In a search for etiologic clues, a review was made of death certificates of residents in a cluster of Louisiana parishes, mainly in the southern part of the state, where lung cancer mortality was high. A comparison of the statements on occupation for 3,327 patients with lung cancer and those of 3,327 controls (matched by sex, race, age, and parish of residence) during 1960-75 revealed an approximately twofold excess risk associated with transportation equipment manufacture, mainly shipbuilding, and the fishing industry. Smaller elevations of lung cancer risk were found among older men who had been employed in petroleum exploration and production and among male and female residents of towns where the petroleum industry was a major employer. In addition, Acadian ancestry was associated with a higher risk of lung cancer among older male and female residents.