Studies designed to test the ability of environmental pollutants to induce lung cancer in experimental animals by chronic inhalation exposure are summarized in this review. The studies are limited to those published in peer-reviewed journals and may not include all experiments conducted by chemical or pharmaceutical manufacturers to test product safety. These studies are also limited to those using small laboratory animals, e.g., Syrian Golden hamsters, mice and rats. The advantages and disadvantages of these species for use in respiratory carcinogenesis studies are discussed. Chemical substances reviewed include organic compounds, inorganic metallic and nonmetallic compounds, and complex mixtures. The results of these studies have shown that cancer of the respiratory tract can be induced by a wide variety of chemicals, many of which are present in ambient air. With few exceptions, substances that have been shown to induce lung cancer in humans have also proven to be carcinogenic in laboratory animals.