  On a high mobility two-dimensional hole gas (2DHG) in a GaAs/GaAlAs
heterostructure we study the interaction correction to the Drude conductivity
in the ballistic regime, $k_BT\tau /\hbar $ $>1$. It is shown that the
'metallic' behaviour of the resistivity ($d\rho /dT>0$) of the low-density 2DHG
is caused by hole-hole interaction effect in this regime. We find that the
temperature dependence of the conductivity and the parallel-field
magnetoresistance are in agreement with this description, and determine the
Fermi-liquid interaction constant $F_0^\sigma $ which controls the sign of
$d\rho /dT$.
