Spin-lattice relaxation times (T1) of water protons and cross-relaxation times (T(IS)) between irradiated protein protons and observed water protons were measured to study water structure in various rat brain tissue. A tumour-bearing rat model and an incomplete forebrain ischaemia model of stroke prone spontaneously hypertensive rats (SHRSP) were used for the experiments. T(IS) and T1 were measured by the inversion recovery FT method with and without f2-irradiation at 7.13 p.p.m. and gamma H2/2 pi approximately 69 Hz, respectively, using a 360 MHz FT-NMR spectrometer. All of experiments on T1 and T(IS) yielded a single kind of component. In spite of small changes in T1 and water content, T(IS) values in peritumoural oedematous and ischaemic brain tissue were significantly shorter than those of normal brain and far shorter than those of brain tumour, indicating a large amount of hydration of marco-molecules in the oedematous and/or ischaemic rat brain tissue. T(IS) might be sensitive parameter for studying the water structure in various brain tissue.