What idiosyncratic consumption risks can counties trade away on international asset markets? This paper develops an empirical methodology for answering the question. The tests are based on the proposition that in an integrated world asset market with representative national agents, the ex post difference between two countries' intertemporal marginal rates of substitution in consumption is uncorrelated with any random variable on which contractual payoffs can be conditioned. This result is applied to annual time-series data for the seven largest industrial countries over 1950-88. Of these counties, Germany seems to have been most successful at internationally diversifying its consumption risks.