This study attempts to test the hypothesis that involuntary exposure to tobacco smoke increases the risk of lung cancer. It is a population-based case-referent (control) study of women who never used tobacco products and develop lung cancer. Cases will be rapidly ascertained in five large metropolitan areas: New Orleans, Atlanta, San Francisco, Los Angeles, and Houston. There will be two separate control groups: non-smoking women who develop colon cancer reesiding in the same geographic area as the cases; and a population control group obtained by a random digit dialing protocol. Personal interviews at home will be conducted. The questionnaire will cover passive smoking exposures at home, at work, and in other areas; residential chracteristics; diet; and demographic information. Logistic regression techniques will be used in the analysis to examine risk of lung cancer associated with passive smoking while controlling for confounding variables. The data processing will be centralized in one of the participating centers, Atlanta, and the analysis will be a cooperative effort of the investigators.