The high-pressure, high-temperature He-3 labeling procedure previously used with C-60 and C-70 was applied to mixtures of isomers of the higher fullerenes C-76, C-78, and C-84. Sufficient helium was introduced inside them to allow helium NMR spectra to be obtained. Each isomer yields a single, sharp, characteristic NMR peak resolved from the others. Our results show that there are more isomers of these fullerenes than previously reported. Three C-78 isomers and three C-84 isomers have been described, but we have shown that there are at least five C-78 isomers and nine C-84 isomers.