The data source of a mailmerge in Word must be a "flat" file.
If you have Access, copy and paste the spreadsheet data as a table in
Access, then use a Query to group the records by customer and do the
summation for each. Then use that Query as a data source.

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Hope this helps,
Doug Robbins - Word MVP
>I am attempting to merge an Excel List (from a Quickbooks
> report) into a Word Main Doc. I have auto summed the
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> How can I get only one letter per customer? Thanks
> Allison