Sam is correct. An ASP.NET DropDownList (there is not native combo box) is emitted and rendered as a standard HTML <select> element. This only allow a single string for it's value and display text. There are numerous 3rd party controls that provide combo box-like behavior for web apps however. You can also use the "poor-mans" approach and set your DDL to use a fixed width font and space delimit mutiple values so they appear tabular.