Adjuvant activity and immunostimulating complex (ISCOM) formation by a series of saponins and glycoalkaloids differing in the structures of their aglycones and sugar chains were examined. The only two saponins apart from Quillaia that were adjuvant-active were Gypsophila and Saponaria, which resemble Quillaia in that they contain saponins with branched sugar chains attached to positions 3 and 28 of the aglycone. Glycoalkaloids with a branched sugar chain lacked adjuvant activity. Saponaria saponins formed irregular ISCOM-like structures, and Gypsophila produced a sheet of joined pore-like structures. The alfalfa hederagenin saponin and Quinoa also formed pore-sheets, despite lacking adjuvanticity.