Nesting countif functions

Can anyone help on how to properly write a function to count the number of
cells in a column with a certain value if they have a corresponding value in
a different column?  For example, I want to count how many times "BIG"
appears in Column B, if the same row has "B" in Column A.
A	B
1	B	BIG
2	C	BIG
3	C	SMALL
4	D	SMALL
5	B	SMALL
6	F	MEDIUM
7	F	BIG
8	E	SMALL
9	E	MEDIUM
10	D	BIG
11	C	BIG
12	B	SMALL
13	C	MEDIUM
14	E	SMALL
15	A	SMALL
16	F	MEDIUM
17	D	SMALL
18	A	BIG
19	B	SMALL
20	C	BIG

Thanks!
Evan

Try this formula...

Try this formula...

=SUMPRODUCT((A1:A100="B")*(B1:B100="BIG"))

The top end of the ranges (A100, B100) can be made to cover any span you may
have now or in the future.

Rick