asp server controls in the form of string

Hi, I need to dynamically load all the controls on to a page. Most of the controls are either radio buttons or checkboxes and the web page basically is a questionaire. I am concatenating all the radio button items in a function in my class. The function returns the concatenated text(in the form of string) to the UI page . I am using asp controls like while concatenating. The text is being displayed but not the radio buttons. Can't I concatenate the asp server controls and return them as a string ? Why is it the radio buttons are not being displayed. Please help! Thanks..