We present a study of the dependence of the hole-spin relaxation on the electron density in an n-modulation-doped 75-angstrom GaAs/AlxGa1-xAs quantum well by using cw and time-resolved photo-luminescence techniques, at low temperature. The electron concentration has been continuously varied from 10(11) to 10(12) cm-2. A slow hole-spin relaxation time has been found (almost-equal-to 1 ns). A polarization decrease has also been observed when the in-plane wave vector of the photocreated holes increases. Calculations are presented which qualitatively support the latter experimental findings.