A 2D-NMR method based on zero-quantum filtered (ZQF-) TOtal Correlation SpectroscopY (TOCSY) was applied to measure 13C-enrichments in complex mixtures of 13C-labeled metabolites generated in carbon-labeling experiments. Using ZQF-TOCSY, more than 30 13C-enrichments could be potentially measured from the analysis of a biomass hydrolyzate prepared from Escherichia coli cells grown on a mixture of 20% [U-13C]-glucose and 80% [1-13C]-glucose, without need for separation of metabolites. The method is applicable to biomass hydrolyzates, cell extracts, and other complex biological samples. It is also applicable to any combination of labeled substrates and provides a basis for examining non-steady-state conditions.