>>>>As I move up and down the list in the combo box the selection under the cursor highlights. At the point the list item highlights I would like to run a procedure that displays the description of the item as a tool tip text.
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>>>This is not going to work, because InteractiveChange() fires only when you actually click on the item in dropdown portion of combobox, not when you are moving the mouse cursor over it.
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>Yes it will work, since the request was for an action to occur when you move up and down the list - not when the mouse cursor is moved.

No, it will not. :) There are actually 2 parts in it.

First, the code in InteractiveChange() will fire and change combo.ToolTipText property only when you drop down the combo and move there with the keyboard, or if you click on item (but not when you move the cursor over dropped down combo portion and when the highlighted item under it changes).

Second - actual ToolTiptext showing. Tooltiptext shows only when you moved the mouse over the control (and disappears in a while). As soon as you move the cursor over dropped down part - you are out of actual control and Tooltiptext does not show. If you move the highlight bar in the dropdown portion with the keys -Tooltiptext disappears along with the mouse cursor.

>How would you do that, BTW? (Not sarcastic - real question)

I would not use tooltiptext. It is not effective and not reliable for the given purpose.