Oriented thin films of the defect perovskite (\mathrm{LaCuO}{3-\delta}) (LCO) have been grown on ( (1(1)) ) Srilio, sulsstrates by pulsel laser depusition. 'The orthorhombic, oxygen-deficient (\mathrm{La}{2} \mathrm{Cu}{2} \mathrm{O}{5}(\delta=0.5)) phase, which is the end-member of the perovskite series, is formed at a growth temperature of (700^{\circ} \mathrm{C}) under (200 \mathrm{mTorr}) background (\mathrm{O}{2}) pressure. With additional oxygen uptake during cooldown, the orthorhombic phase can be easily converted to the monoclinic modification ( (\delta \leq 0.4) ). The more highly oxygenated tetragonal phase ( (\delta \leq 0.2) ) is, however, not obtained for background (\mathrm{O}{2}) pressures up to 760 Torr. Partial conversion to the tetragonal phase has been achieved by postannealing the films at (600-650^{\circ} \mathrm{C}) under high oxygen pressure ( 450 bar). From resistivity measurements, a distinct insulator-metal transition is observed in going from the orthorhombic to the monoclinic structure, with postannealed films containing the mixed tetragonal and monoclinic phases showing the lowest resistivity. However, no evidence of superconductivity has been detected in any of the films down to (5 \mathrm{~K}). 1994 Academic Press, Inc.