  We report measurements of the spin susceptibility in dilute two-dimensional
electrons confined to a 45$\AA$ wide AlAs quantum well. The electrons in this
well occupy an out-of-plane conduction-band valley, rendering a system similar
to two-dimensional electrons in Si-MOSFETs but with only one valley occupied.
We observe an enhancement of the spin susceptibility over the band value that
increases as the density is decreased, following closely the prediction of
quantum Monte Carlo calculations and continuing at finite values through the
metal-insulator transition.
