Unfractionated GPI-0100 (UFGPI-0100) containing semi-synthetic derivatives of deacylated Quillaja saponins (DS saponins) modified at the glucuronic acid residue was resolved by reverse phase low-pressure liquid chromatography (RP-LPLC) into two fractions, RP18-1 and RP18-2, with different compositions and adjuvanticity. The fraction RP18-1 contained DS saponin adducts of N-dicyclohexylurea, and stimulated Th2 immunity with production of IgG1, while the RP18-2 fraction contained the dodecylamide derivatives of DS saponins and stimulated Th1 immunity with production of IgG2a, IFN-γ, IL-2, and CTL. The strong immune stimulatory properties of RP18-2, relative to RP18-1, and the formation of RP18-1/RP18-2 mixed micelles may account for the effective stimulation of Th1 immunity by UFGPI-0100. UFGPI-0100 was free of acylated quillaja saponin components, including the more stable QS-7. © 2003 Elsevier Science Ltd. All rights reserved.