Macromolecule resonances underlying metabolites in 1H NMR spectra were investigated in temporal lobe biopsy tissue from epilepsy patients and from localized 1H spectra of the brains of healthy volunteers. The 1H NMR spectrum of brain tissue was compared with that of cytosol and dialyzed cytosol after removal of low molecular weight molecules (< 3500 daltons) at 8.4 and 2.1 Tesla. The assignment of specific resonances to macromolecules in 2.1 Tesla, short-TE, localized human brain 1H NMR spectra in vivo was made on the basis of a J-editing method using the spectral parameters (delta, J) and connectivities determined from 2D experiments in vitro. Two prominent connectivities associated with macromolecules in vitro (0.93-2.05 delta and 1.6-3.00 delta) were also detected in vivo by the J-editing method. Advantage was taken of the large difference in measured T1 relaxation times between macromolecule and metabolite resonances in the brain spectrum to acquire 'metabolite-nulled' macromolecule spectra. These spectra appear identical to the spectra of macromolecules isolated in vitro.