The Mann-Kendall rank correlation test was performed to detect trends in this study. The research investigated 3 annual stream-flow variables including annual instantaneous minimum, mean and instantaneous maximum streamflows for a network of 57 Turkish streamflow gauging stations in 25 basins of Turkey, during 1968-2007. The application of trend detection technique to 3 stream-flow variables has resulted in the identification of significant decreasing trends at the 0.05 level, appearing mostly in the basins in western and partly in southeastern Turkey, whereas almost no evidence of significant change was experienced with a general downward direction in the rest of the country. Of the 25 basins, however, only basins with the numbers of 12 and 22 exhibited significant increasing trend for one station each. The number of stations showing a decreasing trend is more than 9-fold that of stations with an upward trend whereas the significant downtrend exceeded the uptrends 49-fold. Besides, almost 2/3 of the decreasing trends (144 times over 159) were found to be statistically significant while approximately 13% of the increasing trends (15 times) exhibited significant trend.