To assess the potential clinical utility of in vivo proton magnetic resonance spectroscopy (MRS) in patients with various endometrial lesions. Twelve patients with untreated uterine bleeding were included in this study. In- vivo proton MRS was performed using a 1.5 T MR scanner. The metabolite levels were classified into three classes in comparison with the noise level by visual examination. All the patients have endometrial biopsy. For each type of lesions, chemical compound were described. Pathological examination resulted in three endometrial cancer, two simple hyperplasias, one complex hyperplasia, two partial hydatiform mole, two proliferative endometrium and two secretory endometrium. In women with endometrial carcinoma, high choline and lipid signals were detected, whereas no creatine and no lactate signals were found. In women with endometrial hyperplasia, choline signal was detectable in all cases but one case showed lactate signal in addition to choline. In women with partial hydatidiform mole, the only detectable signal was choline. Lipid signals were detected in none of the cases with endometrial hyperplasia and partial hidatidiform mole. In women with either secretory or proliferative endometrium, choline and lactate signals were detectable in all cases but one case showed solely choline. Lipid signals were not deteced in any of subjects with secretory or proliferative endometrium. The observed difference is the presence of lipid signal only in endometrial carcinoma.