A well recognized hazard of conservative surgical treatment of tubal pregnancy is incomplete removal of trophoblastic tissue. Persistent trophoblast can be detected by postoperative serum human chorionic gonadotrophin (HCG) monitoring. The impact of various surgical techniques on the post-operative clearance of serum HCG was investigated in a retrospective study. The medical records of 97 patients treated surgically for tubal pregnancy in the Academic Medical Center of the University of Amsterdam, The Netherlands, between 1 January 1992 and 1 August 1994 were reviewed; 28 patients were treated by salpingostomy by laparoscopy, 16 by salpingostomy by open surgery and 53 by salpingectomy by either method. There was no difference in the post-operative clearance of serum HCG after successful conservative surgery compared to radical surgery. However, persistent trophoblast occurred in eight patients (29%) after laparoscopic salpingostomy and in only one patient (6.3%) who had a salpingostomy by open surgery (relative risk 4.57). Serum HCG clearance curves allow early identification of patients with persistent trophoblast after conservative surgical treatment. Moreover, monitoring of post-operative serum HCG until it becomes undetectable is mandatory in order to reveal late-onset types of persistent trophoblast.