Thanks for answers, the const ptr was a fault. Well, the following example shows the problem in detail: ----8<---- #include <iostream> #include <boost/shared_ptr.hpp> struct Spec { Spec(const char* n) : m_name(n) { } void member() const { std::cout << "Hold " << m_name << std::endl; } const char* m_name; }; struct SpecLP : public Spec { SpecLP(const char* n) : Spec(n) { std::cout << "construct " << m_name << std::endl; } ~SpecLP() { std::cout << "destruct " << m_name << std::endl; } }; struct SpecHP : public Spec { SpecHP(const char* n) : Spec(n) { std::cout << "construct " << m_name << std::endl; } ~SpecHP() { std::cout << "destruct " << m_name << std::endl; } }; struct Doc { virtual ~Doc() { } virtual void set(boost::shared_ptr<Spec>& ptr) = 0; }; struct LpDoc : public Doc { LpDoc() : m_lp( new SpecLP("LpDoc::lp") ) { } void set(boost::shared_ptr<Spec>& spec) { // m_lp = boost::shared_static_cast<SpecLP>( spec ); m_lp = boost::shared_polymorphic_cast<SpecLP>( spec ); } void print() { m_lp->member(); } boost::shared_ptr<SpecLP> m_lp; }; struct HpDoc : public Doc { HpDoc() : m_hp( new SpecHP("HpDoc::hp") ) { } void set(boost::shared_ptr<Spec>& spec) { // m_hp = boost::shared_static_cast<SpecHP>( spec ); m_hp = boost::shared_polymorphic_cast<SpecHP>( spec ); } void print() { m_hp->member(); } boost::shared_ptr<SpecHP> m_hp; }; int main() { boost::shared_ptr<Spec> lp( new SpecLP("lp") ); boost::shared_ptr<Spec> hp( new SpecHP("hp") ); LpDoc doc; std::cout << "Case 1:\n"; doc.print(); doc.set( lp ); // is O.K. doc.print(); std::cout << "Case 2:\n"; try { doc.print(); doc.set( hp ); // should throw doc.print(); } catch(const std::bad_alloc& e) { std::cerr << "Exception \"" << e.what() << "\" catched\n"; } } ---->8---- It doesn't compile with shared_ptr. Imho is the polymorph code correct expect the pointer problem. Thanks Olaf