We report evidence on the profitability and statistical significance among 2,127 technical trading rules. The best rules are found to be significantly profitable based on standard tests. We then employ Whiteâs (2000) Reality Check to evaluate these rules and find that data-snooping biases do not change the basic conclusions for the full sample. A sub-sample analysis indicates that the data-snooping problem is more serious in the second half of the sample. Profitability becomes much weaker in the more recent period, suggesting that the foreign exchange market becomes more efficient over time. Evidence from cross exchange rates confirms the basic findings.