Binary data in postgres

Is it possible to store and restore (!) binary data in a postgres
database.
The 'Programmer's Guide' sais, there is a method
int PQbinaryTuples(PGresult *res);
which returns 1 if there is binary data in the result.
But how can I say postgres to save something in a binary style?
The result is allways NOT 1!

Thanks, Tim