  We present results on an analysis of the decay constants fB and fBs with two
flavours of sea quark. The calculation has been carried out on 3 different bare
gauge couplings and 4 sea quark masses at each gauge coupling, with m_pi/m_rho
ranging from 0.8 to 0.6. We employ the Fermilab formalism to perform
calculations with heavy quarks whose mass is in the range of the b-quark. A
comparison with a quenched calculation using the same action is made to
elucidate the effects due to the sea quarks.
