The present invention provides a method, apparatus, and computer instructions for dynamic intermediate code transformation in a mixed mode compiler. In an exemplary embodiment, an object code compiler of a virtual-machine, such as the just-in-time (JIT) compiler (415) of a Java virtual machine (JVM), takes loaded classes and compiles these into object code (416). A JIT-enabled dynamic instrumentation (JEDI) interface (420) provides information to an application (e.g., a tool with a GUI), and passes requests for transformation to the JIT (415) and class-loader (410). If loaded, JEDI controls the JIT compiler (415) to compile and transform the class into object code. Thus, dynamically transformed object code is produced without transformation or re-loading of the loaded classes.