  A detailed investigation of the metallic behaviour in high quality
GaAs-AlGaAs two dimensional hole systems reveals the presence of quantum
corrections to the resistivity at low temperatures. Despite the low density
($r_{s}>10$) and high quality of these systems, both weak localisation
(observed via negative magnetoresistance) and weak hole-hole interactions
(giving a correction to the Hall constant) are present in the so-called
metallic phase where the resistivity decreases with decreasing temperature. The
results suggest that even at high $r_{s}$ there is no metallic phase at T=0 in
two dimensions.
