Although the vascular system is presently being imaged by multiple high technology modalities, contrast angiography continues to be the gold standard; however, severe complications rarely occur. During the last 25 years (in over 1400 patients), CO2 has proven to be extremely safe (no allergy or renal failure). However, it is imperative to understand CO2's physical properties and potential dangers. Recently, CO2 is being routinely utilized not only because of safety, but for detection of minute amounts of bleeding, better collateral filling, and for most interventional procedures since unlimited volumes of CO2 can be injected between the catheter and guidewire. Presently, safe, reliable and "user-friendly" delivery systems are now commercially available. CO2 DSA images are now nearly comparable to iodinated contrast, and improvement in DSA images are evolving, including "stacking" software.