In 1909 the US Department of Agriculture (USDA) established a research station known as Camp Del phinium in the Gunnison National Forest near Gunnison, Colorado (Fig. 1). The purpose of this station, under the direction of Dr C. D. Marsh, was to study and find solutions to larkspur poisoning in cattle. As a result of this work, Farmers Bulletin 531, entitled Larkspur or Poison Weed, was published in 1916 detailing the current knowledge of larkspur intoxication in livestock, including management recommendations and treatment of intoxicated animals. Although much has changed in the livestock industry since 1909, larkspur poisoning is still a significant problem on ranges where it occurs. During the 100 years since the beginning of larkspur research by the USDA, numerous studies have been undertaken to solve the problem of larkspur poisoning in cattle, culminating in work currently underway at the Agricultural Research Service's Poisonous Plant Research Laboratory (PPRL) in Logan, Utah. The purpose of this article is to review important past findings and to highlight current research on larkspur at the PPRL. Delphinium (larkspur) species are members of the Ranunculacae family of plants that are commonly known as the buttercup family. Toxic larkspurs are found in the High Plains, foothill, and mountain rangelands of the western United States. The toxins in larkspurs are alkaloids, nitrogen-based compounds with potent pharmacological effects. Although the scope of the problem caused by toxic larkspur varies from year to year, the overall losses of cattle due to larkspur have remained remarkably consistent over time. For example, Marsh et al.1 described losses averaging 5% with some ranchers losing up to 200 head in a single season. More recently Pfister et al.2 have documented losses ranging from 2% to 5% and as high as 15% in places with large stands of toxic larkspur. Although the death of livestock is an obvious contribution to total dollar value losses, there are additional factors that must be considered. For example, stocker cattle grazing on typical rangeland where toxic larkspur grows have the potential to gain up to 2.5 pounds per day (1.1 kg/day), and many producers, upon losing animals to larkspur, move them off ranges that have high-quality forage. This results in significant amounts of wasted high-quality forage and increased feeding costs. Other hidden costs include the loss of lactating cows from larkspur poisoning. The loss of a cow typically leaves an early weaned, poorly performing calf and requires a replacement cow or heifer to be found if herd numbers are to stay constant.