Benzene is a known carcinogen. It affects white blood cells; it causes leukemia and aplastic anemia. It may also affect the immune system which is dependent on white blood cells.1 It has been removed from all household products, but it is still present in gasoline. Alaskan gasoline is particularly high in benzene (>5%). Gasoline refined in Alaska has high concentrations of benzene and other the aromatic compounds as much as 50% aromatics by volume. Leaving the aromatics in the gasoline helps cars start in the cold, but it also puts high concentrations of benzene in both the ambient and indoor air. We already knew from previous work done in Alaska by Bernard Goldstein in Valdez2 and the Anchorage Department of Health and Human Services in Anchorage3 that people were exposed to high ambient levels of benzene in the winter, and that there were high indoor benzene concentrations in homes with attached garages if the garage was used to store gasoline or gasoline powered engines. Benzene does not bioaccumulate in the body as dioxin or some pesticides do. But are its effects cumulative? Does a little dose of benzene everyday have the same effect as a large dose over less time? Benzene reduces CD4 cells in a dose-response manner at workplace concentrations less than 1 ppm (OSHA 8-hour exposure limit) in workers.4 People who live in homes with high benzene concentrations may be exposed 24 hours a day, seven days a week. There have been no studies of health effects of such environmental exposure to benzene. This study was done to determine three things: 1. What percentage of Anchorage homes with attached garages had high levels of indoor benzene? 2. Were the high levels of indoor benzene affecting the health of the residents? 3. Were residents more likely to develop asthma in homes with high levels of indoor benzene?