<<<<< HELP from BRAZIL

Dear Bretai2k, Good Morning.

It´s very important always, the user attach here a worksheet with an example about your question.
It´s quicker, easier and all the answers are effective on the solution.

At first time you said:
"...Originally Posted by Bretai2k
I have 2 dropdowns (A2 and B2) on sheet 1 that both reference cells B2 through B75 on sheet 2. I want to be able to do a SUM of all cells in the B column of sheet 2 between what I select in dropdowns A2 and B2.
I can provide examples if this is not clear enough.TIA ..."

Then, the formula was built pointing to these cells.
=SUM(INDIRECT(CONCATENATE("Sheet2!$B",MATCH(A2,She et2!$B$2:$B$75,0)+1,":$B",MATCH(B2,Sheet2!$B$2:$B$ 75, 0)+1))

NOW, you´re saying this:
"...The actual range of cells I want to validate against is on Sheet1, cells B2 through B75, while the function is checking the start and end of the range on sheet 2, cells A2 and B2...."
Then you need to invert the formula.

Put on any cell on SHEET2 this fórmula:
=SUM(INDIRECT(CONCATENATE("Sheet1!$B",MATCH(A2,She et1!$B$2:$B$75,0)+1,":$B",MATCH(B2,Sheet1!$B$2:$B$ 75, 0)+1))

Is this working for you now?