In standards compliant browsers (IE might have some sort of option), there is no way of doing this without resorting to JavaScript. However, I think that using mouse wheel on the combo box is a common functionality that most users expect and I for one would not like it if a website would prevent me from using that functionality. What you think is the best for the users is not always what they think is best. A safe bet is letting the user decide. If they want to scroll in combo boxes via mouse wheel, let them, if they don't they won't do it.