Technical Abstract: The low larkspurs (Delphinium nuttallianum and D. andersonii) are two toxic plant species that are often fatally ingested by cattle on western U.S. rangelands. To assess the potential toxicity of the plants, methods are needed to identify and quantify the toxic N-methylsuccinimidoanthranoyllycacontine type alkaloids in the plant. The objective is to compare normal phase and reverse phase HPLC-MS methods of analysis for detection and identification of toxic alkaloids in two species of toxic larkspur plants. Define the toxic alkaloids found in Delphinium nuttallianum and D. andersonii collected from several sites in the western United States. The major toxic alkaloids found in the low larkspurs included methyllycaconitine, nudicauline, 14-deacetylnudicauline, and geyerline. Other toxic alkaloids detected at lower concentrations included 16-deacetylgeyerline, gradiflorine, bearline, 14-acetylbearline, barbinine, 16-demethylnudicauline and three additional isomers of bearline. Total toxic alkaloid concentrations ranged from 0.72 mg/g (d.w.) to 7.02 mg/g determined by reverse phase HPLC-MS. The low larkspurs contain a number of toxic alkaloids in addition to the alkaloid methyllycaconitine that need to be assessed when considering the toxicity of the plant. Both normal phase and reverse phase HPLC methods are adequate to detect and quantify the alkaloids. The reverse phase separation may be preferred due to readily available columns, reduced solvent use and simplicity of the electrospray ionization source.