>And the winner is (roll the drums): David Frankenbach!
>
>Here are the result on a smaller record set (500 records):
>- David Frankenbach: 20.750 seconds
>- Mark Mccasland: 21.611 seconds
>- Josh Weiss: 26.779 seconds
>- My original program: 130.317 seconds
>
>Rich Addison and Brad St. Germaine idea don't apply to my problem at hand because I need to check for duplicate in the SDF file itself, not with the master table.
>
>With David solution, I estimate that the total time needed to import 42 485 records will be around 30 minutes instead of the 3 hours with my original idea!
>
>I was surprised by Josh result: I didn't think that it would make that difference between a Rushmorized (!!!) LOCATE and a IndexSeek(). Even the Seek() was faster than the LOCATE.
>
>Anyway, thanks to everyone for their much appreciated ideas.

Unless I've completely misunderstood, the same logic applies to your SDF file.
testtim SDF file = 2505 records with 1490 non-duplicate records, in other words, the file has 1015 duplicate records in the SDF file.

Code :
USE c:\brad\testtim3 ORDER telephone EXCL
USE c:\brad\testtim2 IN 0 EXCL
lctime = SECONDS()
SELECT testtim2
APPEND FROM c:\brad\testtim.txt TYPE SDF
SET RELA TO telephone INTO testtim3
SCAN
IF !FOUND('testtim3')
INSERT INTO testtim3 ;
(telephone) ;
VALUES ;
(testtim2.telephone)
ENDIF
ENDSCAN

?SECONDS() - lctime

After running the above code on a P166 with VFP5.0a, time taken was .4 to .5 seconds to process 2500 records and to have a table with no duplicate numbers in it.
Again, if I've misunderstood what it is you're trying to get at, my apologies.
Brad