We determined the po toxicity of tall larkspur (Delphinium barbeyi) of known alkaloid composition to cattle. We calculated the effective dose at which the alkaloids methyllycaconitine and 14-deacetylnudicauline, collectively termed total toxic alkaloid, caused collapse and sternal recumbency. The effective dose of total toxic alkaloid that produced sternal recumbency in steers was 11.2 mg/kg bw. Based on this dose, we hypothesize that the LD50 for a po dose of total toxic alkaloids in cattle will be 25 to 40 mg/kg bw.