The members of the Bacillus cereus group, Bacillus anthracis, Bacillus thuringiensis, and B. cereus senso stricto, are largely defined by their content of large plasmids, which encode major virulence factors. Here we offer an easy, fast, and reliable protocol for the isolation and detection of large plasmids up to the size of at least 350kb. Furthermore, using this method, we report that Bacillus mycoides contain large plasmids.