Like everyone else I'd advise an array rather than individually names scalars. I add the twist of using constants to give the individual elements of that array meaningful names.

use constant CODE=>0;
use constant SUBCODE=>1;
...
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If your using 5.8 then your can combine the constant declarations into one

use constant {
    CODE=>0, SUBCODE=>1, ....
};
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Your code can then read something like this

if( $response[CODE] == 20 and 
     $response[SUBCODE] == 55 ) {
     # Do something appropriate
}
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Which is nicely self-documenting and efficient to boot.

If your application lends itself to it, then the above test could become

if( "@response[CODE, SUBCODE]" eq '20 55' ) {
    # do stuff
}
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which can greatly simplify and clarify coumpound conditionals provided the individual elements don't contain spaces.