  High quality strongly correlated two-dimensional (2D) electron systems at low
temperatures $T\rightarrow 0$ exhibits an apparent metal-to-insulator
transition (MIT) at a large $r_s$ value around 40. We have measured the
magnetoresistance of 2D holes in weak perpendicular magnetic field in the
vicinity of the transition for a series of carrier densities ranging from
$0.2-1.5\times10^{10}$ $cm^{-2}$. The sign of the magnetoresistance is found to
be charge density dependent: in the direction of decreasing density, the sign
changes from being positive to negative across a characteristic value that
coincides with the critical density of MIT.
