Eleven oligosaccharides were purified form the urine of sheep with swainsonine toxicosis induced by the feeding of Astragalus lentiginosus. Oligosaccharides were extracted by charcoal adsorption, chromatographed on Bio-Gel P-2, and partially fractionated by preparative-layer chromatography. Separation into individual compounds was completed by semi-preparative high pressure liquid chromatography. Structures were determined by a combination of high pressure liquid chromatography and exo- and endo- glycosidase action, methanolysis followed by gas-liquid chromatography, methylation analysis, and high resolution nuclear magnetic resonance spectroscopy. Two homologous series of oligosaccharides were identified: (a) alpha-D-Manp-(1----6)-beta-D-Manp-(1----4)-D-GlcpNAc, alpha-D-Manp(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp+ ++-(1----4)-D-GlcpNAc, alpha-D-Manp-(1----2)-alpha-D-Manp(1----3)-[alpha-D-Manp+ ++-(1----6)]-beta-D-Manp-(1----4)-D-GlcpNAc, and alpha-D-Manp-(1----2)-alpha-D-Manp-(1----2)-alpha-D-Manp+ ++-(1----3)-[alpha- D-Manp-(1----6)]-beta-D-Manp-(1----4)-D-GlcpNAc (minor series); (b) alpha-D-Manp-(1----6)-beta-D-Manp-(1----4)-beta-D-GlcpNAc- (1----4)-D-GlcpNAc, alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-beta-D-Manp -(1----4)-beta-D-GlcpNAc-(1----4)-D-GlcpNAc, alpha-D-Manp(1----3)-alpha-D-Manp-(1----6)-beta-D-Manp -(1----4)-beta-D-GlcpNAc- (1----4)-D-GlcpNAc, alpha-D-Manp-(1----6)-alpha-D-Manp-(1----6)-beta-D-Manp++ +-(1----4)-beta-D-GlcpNAc - (1----4)-D-GlcpNAc, alpha-D-Manp-(1----3)-alpha-D-Manp-(1----6)-[alpha-D-Manp -(1----3)]-beta-D- Manp-(1----4)-beta-D-GlcpNAc-(1----4)-D-GlcpNAc, alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-alpha-D-Man p-(1----6)-beta-D- Manp-(1----4)-beta-D-GlcpNAc-(1----4)-D-GlcpNAc, and alpha-D-Manp-(1----3)-[alpha-D-Manp-(1----6)]-alpha-D-Man p-(1----6)- [alpha-D-Manp-(1----3)]-beta-D-Manp-(1----4)-beta-D-GlcpNAc- (1----4)-D- GlcpNAc (major series).