external template classes?

Is there a way to declare a template class externally. I have come across a situation where two such classes use the other as a method parameter, and the only way I can think of doing it is with some kind of external declaration.

template<typename TYPE> class FOO
     {
     bool operator =(const BLAH<TYPE>&); //error, BLAH not yet declared 
     };

template<typename TYPE> class BLAH
     {
     bool operator =(const FOO<TYPE>&); //everything is fine here
     };

As usual, thanks in advance.