The relative configurations of pilocarpine and isopilocarpine, the major alkaloids of jaborandi leaves, have been established as cis and trans, respectively. Degradation of their oxidation product, homoisopilopic acid, to an optically active 2,3-diethylbutane-1,4-diol proves the trans sterochemistry of the iso series. Assignment of absolute configuration is based on (a) conversion of homoisopilopic