Complete dissolution is needed for the separation, characterization or homogeneous labeling of whole starch molecules. A method is presented to quantify the extent of starch dissolution in dimethylsulfoxide (DMSO) for the first time, with 1H NMR using toluene as an internal standard; it is validated on a commercial rice starch. It is used directly on starch dispersions containing possible undissolved or co-dissolved species. High-amylose maize starches, known to be digested slowly in vivo, only quantitatively dissolve in the presence of high concentrations of an H-bond disrupter, LiBr, although they form clear dispersions at low LiBr concentrations. Starch quantitatively dissolves from waxy rice flours; non-starch components partially co-dissolve but do not interfere with the dissolution quantification.