Hi Dimitry, the code Bonnie gave you in your other thread on Interfaces showed you how to find the parent form of your textbox classes - it also showed you how to test for the existence of your method, e.g. if(This.Parent is IEnableDisable) that is the beauty of interfaces - they force you to implement all methods defined in the interface ( even if there is no code in them ) so class MyForm:IEnableDisable wont compile unless you implement all of the methods it contains.