We compared five endoscopic thermal devices that have been used clinically for control of arterial bleeding in the gastrointestinal tract: neodymium:yttrium-aluminum-garnet (YAG) laser, electrofulguration, monopolar and bipolar electrocoagulation, and heater probe. In canine models we determined the ability to coagulate arteries of varying size and depth. The most effective method for coagulation of medium size arteries was first to occlude the vessel by compression, then to apply heat to seal it (coaptive coagulation). For the contact probes (monopolar, bipolar, and heater probes), the depth of tissue coagulation was controlled by varying probe appositional force and energy, and coagulation of deep arteries was possible. Undesirable erosion of tissue and vessels was noted with electrical sparking from the monopolar electrode and with YAG laser at high power density. In contrast, heater probe and bipolar electrocoagulation did not produce tissue erosion at any instrument setting. In this comparative study of arterial coagulation, overall ranking was as follows: heater probe = bipolar electrocoagulation greater than monopolar electrocoagulation greater than neodymium:YAG laser greater than electrofulguration greater than control. In our opinion these data should assist the clinician or investigator who plans to coagulate arterial bleeding lesions such as peptic ulcers, although further clinical research will be needed to verify these experimental results.