Natural abundance Carbon-13 nuclear magnetic resonance spectra at 20 MHz were reported for the three common human milk oligosaccharides, lacto-N-tetraose and lacto-N-fucopentaoses I and II, as well as for two related tetra- and hexasaccharide alditols isolated from the alkaline borohydride degradation products of an ovarian cyst glycoprotein. Spectral assignments made with the help of deuterium-induced shift (DIS), attached proton test (APT), and T1 data indicated some very irregular glycosylation shifts which were attributed to effects of steric crowding and non-nearest-neighbor interactions. Samples as small as 10 mumol of oligosaccharide gave acceptable 20-MHz spectra with the use of a 5-mm probe coil.