It has been difficult to diagnose all but advanced cases of lymph node metastases with CT or MRI. It has been reported that the serum value of CA125 rises with the stage of endometrial cancer. This level is lower in the postmenopausal period than before menopause. In this study, we have examined the usefulness of CA125 for the assessment of lymph node metastasis in 43 postmenopausal endometrial cancer cases. There were significant differences in the CA125 level between lymph node metastasis positive cases and negative cases, between cancers occupying > or = 1/2 and < 1/2 of the uterine cavity, between lesions of > or = 1/3 and < 1/3 depth, and between surgical stages I, and III and IV. There was no significant correlation between serum CA125 levels and histological type. The serum CA125 value (mean +/- S.D., U/ml) was 179.0 +/- 291.0 (N = 6) in cases with lymph node metastasis and 15.8 +/- 8.5 (N = 37) in cases without metastasis (p < 0.001). We concluded that 32U/ml, which equals the mean + 2S.D., is a useful cut off value for suspicion of lymph node metastasis. The sensitivity and specificity of this cut off value were 100 (6/6) and 91.9% (34/37), respectively. This standard seems likely to considerably increase the accuracy of diagnosis of lymph node metastasis when taken in combination with the several factors already known to predict this. It may also be useful to diagnose lymph node metastasis in the preoperative period. Although the number of cases in this study was small, the data seem very promising for planning therapy for individual cases.(ABSTRACT TRUNCATED AT 250 WORDS)