H-2 quadrupolar and one-bond C-13-C-13 dipolar couplings have been measured at methyl sites in a uniformly C-13 and fractionally H-2 labeled sample of the N-terminal drk SH3 domain, weakly aligned in a dilute solution of Pf1 phage. An average ratio between the 2H quadrupolar and C-13-C-13 dipolar couplings of 19.2 +/- 0.1 is measured. Assuming rapid rotation about the one bond (13)Cmethyl-C-13 axis and an angle of 109.5 degrees between the unique principal axis of the electric field gradient tensor and the methyl averaging axis (C-13(methyl)-C-13 bond), an average value of 167 +/- 1 kHz is obtained for the quadrupolar coupling constant, e(2)qQ/h. The profile of H-2 quadrupolar vs C-13-C-13 dipolar couplings suggests that the use of a uniform value for the quadrupolar coupling constant is a good approximation in the analysis of H-2 relaxation data measured at methyl sites in proteins.