Thanks for the prompt response. Unfortunately, still no success. :( The only two classes from the Infragistics.Win.UltraWinDock namespace that have the WindowState property are MdiChildForm and FloatingWindowContainer. I can't cast the parent of the DockableControlPane which I want to maximize to a MdiChildForm, nor the parent of the corresponding DockAreaPane to a FloatingWindowContainer, because these are incompatible types ... One thing I could do, and this is casting the parent of the control which I want in a maximized window (an UltraGroupBox) to a MdiChildForm. But this issued an error at runtime, basically saying that this cast, DockableWindow to MdiChildForm, is invalid. So ... which one is the correct object to set its WindowState property to Maximized and how can I get to it, starting from the UltraDockManager object? Thanks.

I think you're mixing things (or I didn't understand). If you want to use Microsoft MDI you just need to set the WindowState of the child form (which is System.Windows.Forms.Form), and set its MdiParent to the main form.

If you want to use the tabbed mdi manager, the drag an UltraTabbedMdiManager to the form and this will save you from setting the WindowState, but you still need to set the MdiParent.

 I attached a sample

Sorry for not being clear enough. Let me fill in the gaps. I said that I want my application to start with one of its MDI windows maximized. For example, I want the ultraDayView1 window to be maximized when the application starts. Maybe this is where I got you confused. The ultraDayView1 is a DockableControlPane which gets its, default, name from the UltraDayView control it contains. The DockableControlPane has its IsMdiChild and Maximized properties set to TRUE. The window that can be seen behind the ultraDayView1 DockableControlPane is also a DockableControlPane object, configured the same way as ultraDayView1. Both DockableControlPane's are items in the Panes collection of the same DockAreaPane object from the DockAreas collection of an UltraDockManager object. (I am sure you knew this hierarchy :) ) What I want is to maximize the ultraDayView1 DockableControlPane, or its container (I am not sure about that because I am new to this ...), so that it fills the whole space available, like the attached picture shows. Please review my previous post in the light of these comments. I hope it is clearer now. Thank you.

OK, now I have the result I wanted. So I was looking in the other direction ... Thanks a lot, Mike.