Water self diffusion in excised rat lungs has been measured ments using the 90Π-gradient pulse-180Π-gradient using pulsed-field-gradient (PFG) techniques. The apparent diffupulse-echo PFG sequence. They found that the apparent sion coefficient, D app , was measured from a plot of the magnetizadiffusion coefficient, D app (t), decreases from 4 1 10 06 cm 2 /s tion M vs g 2 a to be 4.0 1 10 06 cm 2 /s in the limit of small gdg a , when t is 5 ms to 1.3 1 10 06 cm 2 /s when t is 50 ms. Their where g is the gyromagnetic ratio, d is the duration of the applied findings indicate that the mean square displacement of the gradient pulses, and g a is the applied gradient strength. D app is spins is not proportional to t, but rather is proportional to independent of the diffusion time, t, for values of t between 18 the square root of t. They offered three possible explanations and 106 ms. For larger values of gdg a , an additional smaller value for such apparently ''non-Brownian'' behavior: (1) reof the slope of M vs g 2 a was observed, indicating the existence of stricted diffusion between ''rigid'' walls, (2) diffusion in a other, more slowly dephasing spins. Variation of t revealed that the fractal-like random medium, or (3) the presence of large relative magnetization associated with the more slowly dephasing spins decreases as t is increased. In addition, the relative magneti-internal field gradients g i due to the air/water interfaces. A zation of the slowly dephasing spins decreases as the temperature, model which assumes a Gaussian distribution of internal T, of the excised rat lung is increased. Slow exchange from the gradients predicts a smaller D app (t) for longer t due to cross compartment of the more rapidly to that of the more slowly determs between internal and external gradients; however, the phasing spins may explain some of the observed dependence of observed dependence on t does not match the theoretical the relative magnetizations on t and T. Measurements of water predictions. The cause of the apparently non-Brownian beself diffusion in rat lung at various levels of water content indicate havior was thus left unexplained. We propose that part of a correlation between T 2 components and diffusion components. the t dependence of D app (t) observed by Kveder et al. arises A new technique that combines the PFG with the Carr-Purcellfrom terms involving g 2 i and the cross term between external Meiboom-Gill technique is presented. The application of this and internal gradients. To test this hypothesis, we used a technique to excised rat lung confirms the correlation between T 2 special PFG sequence which eliminates the effect of these and diffusion components.