Just played with it a little- I don't know about pointing out errors, but it does thses things-- 1) If you have a value slider set to 0, it removes it completely 2) If you have a color set in a channel that uses a value (refraction, bump, shininess) it replaces it with a value slider set to the appropriate amount. 3) It collapses unused branches- if you have an add with an empty operand, it removes the add and moves up the one operand you have. All these changes would save time when rendering. I think Optimize trys to make your shader as simple as it can. Cool! I'll have to start using this function! Thanks for pointing it out! Markd