Hi Forrest, IDL has a binary tree implementation under the example section: Using Pointers to Create Binary Trees. This is not an AVL binary tree but it could be a good starting point to implement one. The codes, idl_tree.pro and tree_example.pro, can be found in the examples/doc/language subdirectory of the IDL distribution. I'm not aware of any other binary tree implementation apart of this one for IDL. You could use the C or C++ implementations that out there in the internet and then use the IDL's CALL_EXTERNAL function to call those implementations(for example, in C I found: http://www.nightmare.com/software.html, and in C++: http://www.cmcrossroads.c.../C++/AvlTrees.html). IF you want to use a Java AVL tree (I found this implementation: http://www.cs.fiu.edu/~we...ctures/AvlTree.java) you could then use IDL-Java bridge. The IDL-Java bridge lets you access Java objects within IDL code. Java objects imported into IDL behave like normal IDL objects. I hope this helped, Fernando