Fumigant applicators who, 6 weeks to 3 months earlier, were exposed to phosphine, a common grain fumigant, or to phosphine and other pesticides had significantly increased stable chromosome rearrangements, primarily translocations in G-banded lymphocytes. Less stable aberrations including chromatid deletions and gaps were significantly increased only during the application season, but not at this later time point. During fumigant application, measured exposure to phosphine exceeds accepted national standards. Since phosphine is also used as a dopant in the microchip industry and is generated in waste treatment, the possibility of more widespread exposure and long term health sequelae must be considered. (Copyright (c) 1989 by the American Association for the Advancement of Science.)