Walden-Coleman, A. E., Rajcan, I. and Earl, H. J. 2013. Dark-adapted leaf conductance, but not minimum leaf conductance, predicts water use efficiency of soybean (Glycine max L. Merr.). Can. J. Plant Sci. 93: 13-22. The conductance to water vapor of dark-adapted leaves (g_dark) has been shown to be negatively correlated with whole-plant water use efficiency (WUE) in soybean, but the physiological basis of this relationship is unknown. It is also not clear how g_dark compares with the minimum leaf conductance of wilted leaves (g_min), a trait that has been studied extensively across a broad range of species. We compared g_dark to g_min of soybean leaves and found that g_dark values were consistently much higher than g_min values measured on the same leaves. Also, across seven soybean varieties known to differ for WUE, g_dark but not g_min was correlated with WUE. Thus, g_dark and g_min should be considered distinct traits. We measured g_dark at two different leaf positions, and found that g_dark measured at the lower leaf position (two main stem nodes below the youngest fully expanded leaf) was best correlated with WUE. We then used this method to screen a selection of current commercial soybean varieties adapted to Ontario, Canada, for variation in g_dark. The range in g_dark among the commercial varieties was as broad as that measured previously among more diverse genotypes, suggesting that Ontario soybean varieties might also vary widely for WUE.