Hyperpolarized noble gas (3He and 129Xe) apparent diffusion coefficient (ADC) measurements have shown remarkable sensitivity to microstructural (i.e., alveolar) changes in the lung, particularly emphysema. The ADC of hyperpolarized noble gases depends strongly on the diffusion time (Δ), and 3He ADC has been shown to be anisotropic for Δ ranging from a few milliseconds down to a few hundred microseconds. In this study, the anisotropic nature of 129Xe diffusion and its dependence on Δ were investigated both numerically, in a budded cylinder model, and in vivo, in an elastase-instilled rat model of emphysema. Whole lung longitudinal ADC (DL) and transverse ADC (DT) were measured for Δ = 6, 50, and 100 ms at 73.5 mT, and correlated with measurements of the mean linear intercept (Lm) obtained from lung histology. A significant increase (P = 0.0021) in DT was measured for Δ = 6 ms between the sham (0.0021 ± 0.0005 cm2/s) and elastase-instilled (0.005 ± 0.001 cm2/s) cohorts, and a strong correlation was measured between DT (Δ = 6 ms) and Lm, with a Pearson's correlation coefficient of 0.90. This study confirms that 129Xe DT increases correlate with alveolar space enlargement due to elastase instillation in rats. Magn Reson Med, 2012. © 2012 Wiley Periodicals, Inc.