r3C NMR is currently being exploited for the study of biochemical events in living systems. We have followed metabolic reactions of ‘3C-labeled substrates in suspensions of intact cells (Z-4), in perfused organs (57), as well as in the living rat (8) and guinea pig (9). Because 13C is only 1.1% abundant, 13C NMR observations in the absence of labeling require either longer signal accumulation times, or more concentrated metabolites. Natural-abundance 13C spectra have been obtained from lowconcentration metabolites in various organisms and tissues (10) and excised muscle (II, 12), but many hours of accumulation were required. We have shown that it is possible to obtain strong natural-abundance 13C signals in a few minutes’ accumulation from the high concentration of depot fat in the human arm and in different parts of the rat (8). Hepatic glycogen, which is concentrated in the liver of the fed animal, has been observed with natural-abundance i3C NMR at 8.5 T with good signal-to-noise in excised liver (13) and in perfused liver ( 7). It has also been observed in phosphorylase kinase-deficient living rats at 4.7 T using a surface coil in conjunction with a surgical procedure (14). Sillerud and Shulman (7) have shown that 100% of the “C in hepatic glycogen is observable despite the high molecular weight of this polymer. These results suggest that hepatic glycogen might be easily observed in the normal living animal using a surface coil without surgical intervention; however, a previous study of the living rat done at 1.9 T (13) showed only weak signals from hepatic glycogen. In the present 1.9 T study of the living rabbit we have observed strong signals from liver glycogen under conditions which mimic those under which man might be studied. NMR spectra were recorded with an Oxford Research Systems TMR spectrometer operating at 20.2 MHz for 13C in the pulse-Fourier transform mode. The 13C signals were observed with a two-turn surface coil constructed from 3 mm diameter copper wire. The coil diameter was 4.2 cm. The 90” pulse width for a small sample placed at the center of the coil was 17 psec. The coil was positioned 2.0 cm from the center of the magnet volume of homogeneous field where the liver was positioned. Proton decoupling was obtained by using a one-turn 8 cm diameter surface coil which was coaxial with the i3C coil. In a phantom experiment adequate decoupling was obtained