  We report the observation of a metal insulator transition at B=0 in a high
mobility two dimensional hole gas in a GaAs-AlGaAs heterostructure. A clear
critical point separates the insulating phase from the metallic phase,
demonstrating the existence of a well defined minimum metallic conductivity
sigma(min)=2e/h. The sigma(T) data either side of the transition can be
`scaled' on to one curve with a single parameter (To). The application of a
parallel magnetic field increases sigma(min) and broadens the transition. We
argue that strong electron-electron interactions (rs = 10) destroy phase
coherence, removing quantum intereference corrections to the conductivity.
