The search for ultra-short-acting intravenous induction agents focused initially on hexobarbital. That methylated oxybarbiturate was discovered in 1932 by German researchers H. Weese and W. Scharpf. Marketed by the Bayer Company in Europe as Evipan, hexobarbital was distributed by New York’s Winthrop Chemical Company as “Evipal Soluble” (above). Hexobarbital has a six-carbon side-ring of cyclohexene. Contrast that with the thiobarbiturate that supplanted hexobarbital: sodium thiopental (branded Pentothal by Abbott Laboratories, USA), which has a five-carbon side chain of pentane. (Copyright © the American Society of Anesthesiologists’ Wood Library-Museum of Anesthesiology.)