We have previously described the structures of four novel unconjugated bufadienolides in the ovary of the toad, Bufo marinus. In this study, we report the separation and characterization of three novel bufadienolide conjugates. These compounds were purified by HPLC, and their structures were determined to be 11alpha, 19-dihydroxytelocinobufagin-3-(12-hydroxydodecanoic acid) ester, 11alpha,19-dihydroxytelocinobufagin-3-(14-hydroxy-7-tetra decenoic acid) ester, and 11alpha, 19-dihydroxytelocinobufagin-3-(14-hydroxytetradecanoic acid) ester on the basis of NMR and MS data. Numerous dicarboxylic acid esters of bufadienolides have previously been described, but the three bufadienolide conjugates described in this report differ from previously described esters in that they contain hydroxylated monocarboxylic acids. The function of these three conjugates is not known but they are, like bufotoxins, potent inhibitors of Na+, K+-ATPase and may play a developmental role in the differentiation of toad oocytes.