The proposed research is an extension of an ongoing chemoprevention trial of beta-carotene and retinol in high-risk asbestos workers. The purpose of the study is to investigate relationships between beta-carotene, retinol and neoplasia of the lung in a high-risk group of persons, mostly men, occupationally exposed to asbestos. The major hypothesis to be tested is: beta-carotene administered in high doses with modest doses of retinol will reduce the risk of progressive atypia and subsequent carcinoma of the lung in humans. Specific objectives are: a. To conduct a randomized, placebo-controlled clinical trial in a group of people at high risk of lung cancer, using beta-carotene and retinol as the chemopreventive agents and bronchial epithelial changes, monitored by sputum cytology, as the primary measure of response. b. To study the prevalence and incidence of cellular atypia in sputum from the high risk group as related to serum levels of beta-carotene. c. To study the effects of long-term beta-carotene and retinol administration and to document the toxicity (or lack of toxicity) through physical examinations, toxicity symptoms questionnaires and serum measurements. Eligible persons were stratified (by age, smoking and asbestos exposure) and randomized to receive either beta-carotene (50 mg/day) and retinol (25,000 IU every other day) or placebo. The duration of treatment was to be three years; with the requested extension, this will be changed to at least six years. Participants are examined in the clinic at six month intervals and monitored between visits by telephone toxicity questionnaires and mail-in sputum specimens.