Hydrodynamical density fingering of chemical fronts separating two miscible, stable steady states of different chemical composition, and hence density, can lead to complex spatio-temporal dynamics. The most striking feature of such dynamics is the disconnection of droplets of one stable steady state from fingers invading the other stable steady state. Such disconnected droplets do not exist in pure density fingering and are thus the result of the bistable kinetics. We study such dynamics by direct numerical simulations of Darcy's law for flow in Hele-Shaw cells coupled to the kinetic equation for the concentration of a chemically reacting solute controlling the density of the miscible solutions. The concentration of this solute obeys a simple cubic model leading to bistability. Experimental realization of such dynamics in spatially extended Hele-Shaw cells calls for the use of the concept of spatial bistability which implies construction of new continuously fed open reactors. (C) 2003 Elsevier Ltd. All rights reserved.