The cardenolide content of the latex and leaves of seven Asclepias species and Calotropis procera was examined quantitatively by spectroassay and qualitatively by TLC. Species relatively rich in cardenolide, such as C. procera, A. curassavica, A. eriocarpa, A. uestita, and A. cordifolia, had latex-leaf cardenolide concentration ratios ranging from 79 (C. procera) to 1.5 (A. cordifolia). Two species, A. californica and A. speciosa, had measurable leaf cardenolide but no measurable amounts in the latex. A. fascicularis had no measurable cardenolide in either leaves or latex. C. procera, A. curussaoica, A. uestita and A. cordifolia had primarily calotropagenin-derived cardenolides, while A. eriocarpa and A. speciosa had primarily desglucosyrioside and its derivatives. The latex of cardenolide-enriched species had greater proportions of lower polarity cardenolides, particularly those with a Spiro NS ring or keto at 3' of the sugar (uscharidin, uscharin, voruscharin. labriformin, labriformidin), than was present in the leaves. Uscharidin, uscharin and voruscharin were isolated from A curassavica latex, and labriformin from A. eriocarpa latex, in higher yields than reported from whole plants.