Pulsed gradient diffusion-weighted spin-echo images (7 to 11 gradient strengths) were obtained in a coronal slice through the midbrain for five normal adult white rats before and after sacrifice in a 2-T CSI system with air temperature control. The pulse sequence was cardiac gated and respiratory synchronized in order to minimize motion artifacts (Tr greater than 2 s. Te = 30 ms). Diffusion coefficients reflecting several tissue compartments (D*) in brain and muscle were calculated and referenced to simultaneously imaged tubes of water. In the living animals, brain cortical matter had a value of D* = (0.82 +/- 0.02) x 10(-3) mm2/s. deeper brain regions had a value of D* = (0.73 +/- 0.02) x 10(-3) mm2/s, and the muscle had a value of D* = (1.4 +/- 0.1) x 10(-3) mm2/s. Postmortem the values in brain dropped by approximately 30%, while remaining constant in muscle. Signal intensity in the spin-echo images for muscle tissue rose by 50% over a 1- to 2-h interval after sacrifice while that of brain tissue remained relatively stable.