How do I create master/detail web pages ussing a session state var ?

HI;
I can create a Master/ Detail relationship between 2 gridviews on 2 different pages using this on Page 1
<asp:HyperLinkField DataNavigateUrlFields="Institution,TypeName" DataNavigateUrlFormatString="OvrDraftContent.aspx?Institution={0}&amp;TypeName={1}" ...