Copper alloys are commonly used in bearings under ambient conditions, but their potential use in aerospace applications with reduced surrounding pressures has not been as extensively investigated. In this study, the sliding friction and wear behaviour of copper alloy CuZn39Pb3 were investigated under both atmospheric and vacuum conditions, with the use of an environmentally controlled pin-on-disk apparatus. Experiments were conducted under pressures of 5 x 10(-3) mbar, 8 x 10(-6) mbar and normal atmospheric conditions (1013 mbar) with contact pressures of 0.3, 1.0 and 2.0 MPa and a 1 m/s constant sliding speed. Scanning electron microscopy was used to characterise the features of the wear surfaces, subsurface regions and debris particles. The wear mechanism of the CuZn39Pb3 alloy was mainly adhesive under both under atmospheric and vacuum conditions; however, some indications of abrasion were observed under atmospheric conditions. The wear rate of the CuZn39Pb3 was lower under vacuum conditions. Furthermore, increasing the applied pressure noticeably increased the wear of the alloy under atmospheric conditions but only slightly increased it under an 8 x 10(-6) mbar vacuum. Extensive subsurface deformation was observed for the alloy tested in air. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.