In many third-quarter conference calls this earnings season, a key question kept popping up: "How are European sales holding up in light of the budding economic crisis?" A wide range of companies noted that sales are starting to slow and things could get worse in coming quarters. GM (NYSE: GM), for example, lost nearly $ 300 million during the third quarter in Europe — a market that accounts for one-fifth of its sales.

With Europe possibly headed for a prolonged economic downturn, it's time to stress test your portfolio and re-think the merit of any holdings that have a high degree of exposure to the continent. To be sure, virtually every company in the S&P 500 has some exposure to Europe. The key questions are: How big is the exposure? And how will profits in 2012 fare if Europe gets mired in a deep slump?

To help in that process, I've drawn up a list of American companies that count on Europe for a big chunk of sales and profits. This group, for example, gets more than 50% of annual sales from Europe.