Adequate endometrial preparation with exogenous steroids is mandatory for successful ovum donation. This study was undertaken to assess the value of endometrial thickness by ultrasound and serum oestradiol as predictors of ovum donation outcome and to analyse the correlation between serum oestradiol concentrations and the endometrial thickness. Endometrial thickness and serum oestradiol concentrations on the day of oocyte donation were recorded and compared to several in-vitro fertilization parameters. The cycles (n = 465) were classified according to serum oestradiol values and endometrial thickness. Comparison of the groups showed that endometrial thickness was significantly (P = 0.002) higher when serum oestradiol was >400 pg/ml as compared to <100 pg/ml. Pregnancy and implantation rates did not differ among the groups, women with serum oestradiol <50 pg/ml having similar outcome to the remaining cases. Endometrial thickness showed a similar picture in terms of pregnancy and implantation. Also, women with an endometrium <4 mm in size had normal pregnancy and implantation rates. There was a positive correlation (P = 0.0044) between endometrial thickness and implantation, as well as between endometrial thickness and serum oestradiol (P = 0.0184). None of the parameters examined was able to predict ovum donation outcome. It is concluded that endometrial thickness is preferred to serum oestradiol for the monitoring of endometrial development, although neither is able to predict success in oocyte donation.