The basic pancreatic trypsin i~ibitor (BPTI) is a well characterized [1,2] small globular protein which functions as an inhibitor of trypsin and other proteases [3]. BFTI was extensively investigated by nuclear magnetic resonance (NMR) techniques [4-g]. In addition to the interest for a better understanding of the structure-function relations in protease-inhibitor systems, these data also provided new insights into general aspects of protein structure and relations between NMR spectral properties and protein conformation. To further pursue these different areas of interest we have started additional investigations using high field 13C NMR at 90.5 MHz. The present paper illustrates the advantages of the high field for the identification of individual resonance lines of protonated carbon atoms, in particular methyl carbons, and reports conformation dependent chemical shifts for numerous methyl 13C resonances in BPTI. While principal aspects of high field 13C nuclear magnetic resonance (NMR) of biological molecules have been much discussed [IO,1 11, relatively few experiments with proteins have so far been reported [ 12141. Much emphasis has actually been on work with extra large sample sizes at the lowest field strength commonly used in high resolution NMR, which were shown to be favorable conditions for studies of non-protonated carbons [15-171. The high field 13C NMR experiments so far mainly included investigations of the field dependence of the spin relaxation times [12,14] and a study of the pH titration of carboxyl groups in lysozyme [ 131. In the