On the day of the scheduled embryo transfer, endometrial biopsies were taken from 53 patients of an IVF-programme. There was subsequent failure of fertilisation in all of these patients. The histologic pattern, compared with reflectivity and thickness of the endometrium was determined sonographically on the same day. All patients had been stimulated with hMG/hCG, and the ovaries and the endometrium had been monitored by transvaginal sonography. The reflectivity pattern was divided into grades (A to D according to Smith et al., 1984) and related to histological findings. The distribution of the grades was as follows: 16 patients (30%) grade A, 22 patients (42 %) grade B, and 15 patients (28 %) grade C. There was no case of grade D in our study. The results of histologic examination for grades A to C were not significantly different from each other. However, in only 37% of grade A, 63% of grade B and 66 % of grade C, the endometrial response corresponded to the state of the cycle. Endometrial thickness for the receptive and non-receptive groups was not significantly different (8.8 +/- 0.29 mm vs. 9.13 +/- 0.4 mm). The results show no correlation between histologic findings and endometrial thickness or reflectivity. We therefore conclude, that sonographic determination of these parameters is not helpful in the evaluation of the degree of endometrial response.