Two groups of patients who were admitted to hospital with a possible diagnosis of ectopic pregnancy were compared. The levels of HCG in the plasma were obtained as an emergency in the first group (45 cases). The levels were not obtained in the second group (34 cases). Only those cases in the first group where the assays had shown the presence of HCG underwent laparoscopy: 12 laparoscopies revealed 7 extra-uterine pregnancies. In the second group, on the other hand, all 34 patients had laparoscopy; only 8 extra-uterine pregnancies were discovered by this method. Because of this study we found that when HCG assays were carried out there was no false positive or negative. When we wanted to rule out an L.H. peak in a doubtful case the assay was repeated. The comparison between the two groups underlines the importance of carrying out the assay: it avoids useless laparoscopies but it also shortens the length of stay in hospital.