I'm guessing that the OP is using xl2007 and wants to know about .xlsb (or
.xls)?
http://www.microsoft.com/interop/docs/officebinaryformats.mspx
or
http://office.microsoft.com/en-us/help/HA100069351033.aspx
From what I've read, the .xlsb binary files open a little faster (less for excel
to do???).
And yep, they can contain macros.
I still use personal.xla in xl2007. I haven't resaved it as .xlab (yet).
> What do you mean by "binary format"?
>
> Pete
>
> > Is there any benifit to using binary format for your workbooks? does it
> > support macros? work fine with addins?

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Dave Peterson