Personally, I have had excellent luck using Retroweaver [http://retroweaver.sourceforge.net/] to back-convert my Java 5 code for deployment on earlier JVM runtimes. Retroweaver can handle *every* linguistic feature from Java 5. (Most of the linguistic changes in Java 5, even generics, have almost no incompatible effects on the compiled bytecode.) You feed it classes compiled with Java 5 and it spits out classes that will work on earlier JVMs. It requires only that you add a small JAR to your classpath. It also combines with the backport-util-concurrent project [http://dcl.mathcs.emory.edu/util/backport-util-concurrent/] to handle java.util.concurrent, Java 5's biggest library enhancement. Except where Java 5 adds new methods (e.g., String.format(...)) to old classes, Retroweaver can handle almost any Java 5 program. I put some back-compiled code through our QA department, which could find no performance or functionality problems. I *strongly* recommend you put in the slight extra effort to run Retroweaver's library-check utility. Point it to your JRE libraries and it will go through the code to ensure it doesn't try to use any methods or classes not available in your JRE (make sure to include the Retroweaver runtime JAR). This will catch those library changes I mentioned that Retroweaver doesn't handle--which is much better than a missing class or method at runtime. If you pass this test, you shouldn't have any problems. I have no affiliation with Retroweaver, though I did submit a patch to the backport-util-concurrent project. I make no claims that it'll work for you, but I'd bet you could run through the LOGBack JAR and get it running on JDK 1.4. If you do, you may want to share your work. Just feed in the LOGBack JARs you need and use the output instead of the original. Andy Gerweck Software Engineer PS: In good conscience, I can't help but recommend you upgrade to Java 5 or higher if at all possible. We're reaching the point where it's bad practice and poor style not to use Java 5's important language enhancements. There are also great runtime advantages, so it's not advisable to force a runtime upgrade where possible. *************************************************************************** The information contained in this communication is confidential, is intended only for the use of the recipient named above, and may be legally privileged. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please resend this communication to the sender and delete the original message or any copy of it from your computer system. Thank You. ****************************************************************************