In vivo estimation of intracranial tumor progression is important in tumor treatment response studies in animal models. High resolution MR images at 4.7 T of 9L-gliomas stereotactically implanted in Fisher-344 rat brains were obtained. Due to elongation of T1 at higher fields, tissue contrast is diminished in T1-weighted images. However, normal anatomy and vasogenic edema are clearly discerned in T2-weighted images (echo times of greater than 50 ms and recycle times of greater than 2 sec). Tumor tissue is not always clearly delineated. Images obtained after administration of contrast agents (Gadolinium DTPA), with short TR (0.6 sec) selectively enhanced the tumorous tissue, with little effect upon normal tissue and edema. Good correlation of enhanced tumor lesions has been observed with histological examination of formalin fixed brains. Relaxation times (T1 and T2) of tumor and normal tissues were measured using stimulated-echo and multi-echo sequences, respectively. Serial images corresponding to tumor growth were recorded, from which tumor volume progression was monitored.