The syntax in your post is right! I think it is because you are testing it in the wrong way. Put the code underneath in a file called redirectTest.asp and request it...
Code:
<%
If Request.QueryString("a") = "" and Request.QueryString("b") = "" Then
Response.Redirect "redirectTest.asp?a=1&b=2"
Else
Response.Write("a: " & Request.QueryString("a") & "<BR>")
Response.Write("b: " & Request.QueryString("b"))
End If
%>
Jacob.