The xyloglucan secreted by suspension-cultured tomato (Lycopersicon esculentum) cells was structurally characterized by analysis of the oligosaccharides generated by treating the polysaccharide with a xyloglucan-specific endoglucanase (XEG). These oligosaccharide subunits were chemically reduced to form the corresponding oligoglycosyl alditols, which were isolated by high-performance liquid chromatography (HPLC). Thirteen of the oligoglycosyl alditols were structurally characterized by a combination of matrix-assisted laser-desorption ionization mass spectrometry and two-dimensional nuclear magnetic resonance (NMR) spectroscopy. Nine of the oligoglycosyl alditols (GXGGol, XXGGol, GSGGol, XSGGol, LXGGol, XTGGol, LSGGol, LLGGol, and LTGGol, [see, Fry, S.C.; York, W.S., et al., Physiologia Plantarum 1993, 89, 1-3, for this nomenclature]) are derived from oligosaccharide subunits that have a cellotetraose backbone. Very small amounts of oligoglycosyl alditols (XGGol, XGGXXGGol, XXGGXGGol, and XGGXSGGol) derived from oligosaccharide subunits that have a cellotriose or celloheptaose backbone were also purified and characterized. The results demonstrate that the xyloglucan secreted by suspension-cultured tomato cells is very complex and is composed predominantly of 'XXGG-type' subunits with a cellotetraose backbone. The rigorous characterization of the oligoglycosyl alditols and assignment of their 1H and 13C NMR spectra constitute a robust data set that can be used as the basis for rapid and accurate structural profiling of xyloglucans produced by Solanaceous plant species and the characterization of enzymes involved in the synthesis, modification, and breakdown of these polysaccharides.