This paper describes a modified P element, P[ry+Δ2-3](99B), in *Drosophila melanogaster* that exhibits unusually high mobilization frequencies while maintaining remarkable stability. The element, constructed by F. Laski, D. Rio, and G. Rubin, has higher transposase activity than an entire P strain but rarely undergoes internal deletion, excision, or transposition. The authors demonstrate that this element can be used for P element mutagenesis, transformation, and transposition. It can substitute for "helper" plasmids in P element-mediated transformation and can move transformed elements around the genome. The high transposase activity of P[ry+Δ2-3](99B) is attributed to position effects and intrinsic properties of the element, while its stability is surprising given its high activity. The element's utility is highlighted in various experimental techniques, including mutagenesis, transformation, and transposition, where it enhances efficiency and stability.This paper describes a modified P element, P[ry+Δ2-3](99B), in *Drosophila melanogaster* that exhibits unusually high mobilization frequencies while maintaining remarkable stability. The element, constructed by F. Laski, D. Rio, and G. Rubin, has higher transposase activity than an entire P strain but rarely undergoes internal deletion, excision, or transposition. The authors demonstrate that this element can be used for P element mutagenesis, transformation, and transposition. It can substitute for "helper" plasmids in P element-mediated transformation and can move transformed elements around the genome. The high transposase activity of P[ry+Δ2-3](99B) is attributed to position effects and intrinsic properties of the element, while its stability is surprising given its high activity. The element's utility is highlighted in various experimental techniques, including mutagenesis, transformation, and transposition, where it enhances efficiency and stability.