Suppose the part numbers are in column A of Sheet1, starting on row 2.
Then in a helper column (eg D2) you can put this formula:
=IF(A2="","-",A2&"_"&COUNTIF(A$2:A2,A2))
and copy it down as far as you like, even beyond your 4000 rows of
data. This will give you a unique sequential number for each serial
number, linked to each part number, like this:
c123_1
c123_2
d123_1
c123_3
and so on. You will get a hyphen where column A is blank, so this
helps to show where you have copied the formula to.
Then on a separate sheet, suppose you use A1 to select the part
number. In B1 you can have this formula:
=IF($A$1="","",IF(ISNA(MATCH($A$1&"_"&ROW(A1),Sheet1!D

,
0)),"",INDEX(Sheet1!B:B,MATCH($A$1&"_"&ROW(A1),Sheet1!D

,0))))
Then you can copy this down as far as you need to - you will just get
blanks if you copy it too far.
Hope this helps.
Pete
On Oct 17, 6:03*pm, LUIS ANGEL <upslavazq...@gmail.com> wrote:
> Hello guys,
>
> I have a BIG *list of part number and serial numbers, in the
> thousands.
>
> In one sheet a have a dropdown box that has all the part numbers. what
> I would like to do is, have the sheet display all the serials of the
> part number I choose from the dropdown box.
>
> So if goe example *I choose part number c123, in some point of the
> sheet all the serials corresponding to c123 will show up.
>
> Any ideas?