We examine how the intrinsic differences between U.S. and non-U.S. stocks affect market participants and the market quality of non-U.S. stocks relative to U.S. stocks. Using proprietary data on NYSE specialist trading, we find that, all else equal, specialist closing inventory positions for non-U.S. stocks are closer to zero than U.S. stocks. The evidence on specialist participation and stabilization rates is mixed. Non-U.S. stocks from developed markets have higher specialist participation and stabilization rates than U.S, stocks, while emerging market stocks have lower participation and stabilization rates than U.S. stocks. With respect to market quality, we find that, all else equal, non-U.S. stocks have wider spreads. less depth, and greater transitory volatility than U.S. stocks. We investigate the reasons behind the difference in liquidity and find that the larger non-U.S. spreads are primarily due to higher information asymmetry and increased adverse selection risk. We conclude that liquidity providers demand greater compensation for trading non-U.S. stocks, but this additional compensation is necessary to offset the higher adverse selection risk. (C) 2002 Elsevier Science S.A. All rights reserved.