I am trying to do something like this in an aspx page: <head runat="server"> <% #if DEBUG %> <script src="jquery-1.3.2.js" type="text/javascript"></script> <% #else %> <script src="jquery-1.3.2.min.js" type="text/javascript"></script> <% #endif %> </head> I get an error "Preprocessor directives must appear as the first non-whitespace character on a line". How can I do this?