The formula should be:

=MATCH(B1,$C$1:$C$300,0)

CountIf needs to look at the whole range C1:C300 for every value.
MATCH will
stop looking further after a success.

Since we are talking of using in conditional formatting, the CountIf
formula
can be shortened to:

=COUNTIF($C$1:$C$300,B1)

The speed difference will still hold though, excepting perhaps no
success
cases.

Have you some details about the
performance difference (or a link to a previous discussion)

[...]

http://www.mrexcel.com/board2/viewtopic.php?t=40233

Aladin
thanks for the information
Frank