If your external reference file is open, then try

=INDIRECT("[" & A1 & "]" & A2)

Where

A1: wb2.xls
A2: Sheet1!A1

INDIRECT() doesn't work on closed files.

In article ,
"ItsMeAgain" wrote:

Can anyone tell me how I might combine to cells to generate a thrird cell
content which calls data from an external reference e.g. I am in wb1.xls and
I have two cells a1 and b1. c1 = a1&b1. a1 = the file name of the external
source, wb2.xls and b1 = the cell reference in wb2. This is so that i can
keep cell rfernces constant but with variable file names. the problem I have
is that I need to make this concatenated cell, c1 operate as =a1+b2 but I
only seem to be able to intorduce the = sign as text.