AbstractMobile genetic elements have been found in the genomes of both procaryotic and eucaryotic organisms. Their unique capacity to move (or transpose) to new chromosomal locations has been critical to their persistence and their ability to affect gene structure and expression. It is conceivable that many physical and chemical agents may induce non‐specific DNA transpositions which can result in genomic rearrangements and mutations. We have derived a simple procedure to detect the induction of DNA transposition using bacteriophage Mu, a temperate coliphage whose 37 kilobase linear double‐stranded DNA genome behaves as a transposable element during lytic growth and lysogeny. Our assay measures the ability of a chemical to enhance or inhibit the induction of Mu DNA transposition and lytic growth. We have examined a wide variety of mutagens, carcinogens and common chemical compounds and found that most of these agents had little effect on prophage Mu induction and lytic growth at all doses tested. However, many DNA‐damaging agents showed a dose‐dependent decrease in both the number of plaque‐forming units and the number of colony‐forming units. We did find that the frequency of prophage Mu induction can be stimulated by certain amino acid analogues, notably azetidine 2‐carboxylic acid, but not by others. These results indicate that the response of mobile genetic elements to external agents is not a simple one, and may reflect the necessary presence of an element and cellular regulatory pathway to control these endoge