Since the late 1990s, shifts in the nature of the global financial integration of developing and emerging countries have exposed them to new forms of external vulnerability. This article explores such in the South African case. The article shows a precipitous growth in the magnitude of South African assets held and traded by international investorsincreasingly institutional investors and 'other' financial institutions, such as hedge funds and complex investment vehicles. The composition of these assets, and the motivation for trading, has also altered, shifting towards a complex set of rand-denominated, short-term assets in equity, bond and derivative markets traded for capital gains. Given this, the article contends that it is the portfolio considerations of such investors, rather than economic 'fundamentals', that have come to determine key economic prices, including the exchange rate, causing volatility, large swings and sudden adjustments. This, it is argued, places monetary policy in a predicament. In the context of liberalised capital accounts, together with the prioritisation of inflation targeting, open-market interventions are ineffective at managing exchange rate movements and volatility, and often reinforce both the patterns of trading and subsequent vulnerabilities while carrying their own costs. In these respects, the nature of South Africa's global financial integrations has exposed it to new forms of external vulnerability, with both these developments, and associated monetary policies, deepening the financialisation of the South African economy.