  The influence of a constant homogeneous external magnetic field $H$ on the
formation and stability of quark droplets is investigated within a simple Nambu
-- Jona-Lasinio model by using a thermodynamic approach. For a vanishing
magnetic field stable quark droplets, which are schematically the bags of
massless quarks, are allowed to exist only at $G>G_{bag}$, where $G$ is the
quark coupling constant, $G_{bag}=1.37G_{crit}$, and $G_{crit}$ is the value of
the coupling constant above which chiral symmetry is spontaneously broken down.
On the other hand, a nonvanishing external magnetic field can induce the
stability of quark droplets so that they may exist even at $G<G_{bag}$. In this
case, depending on the value of $H$, quark droplets are composed either of
massive or massless quarks.
