The 39K contents of isolated pellets and supernatant solutions from suspensions of Halobacterium halobium were studied at 21-22 degrees C by pulsed NMR spectroscopy. The rates of transverse relaxation were measured directly from the free induction decay (FID). The rate of longitudinal relaxation was measured by studying the FID after pairs of pulses of approximately 90 degrees. Care was exercised to minimize the effect of magnetic field inhomogeneity; its contribution to the FID was approximately 25-30 sec-1. The transverse relaxation process was found to consist of at least two components, whose rates were 321-449 sec-1 and 1,122-2,067 sec-1. In one preparation where the longitudinal relaxation process was studied, the data could be well fit to a single exponential relaxing at 253 +/- 33 (mean +/-95% confidence limits) sec-1. Comparison of the relative intensities of the NMR signals with the results of atomic absorption photometric analyses indicated that the great bulk of the intracellular 39K was detected by the NMR techniques used. The data obtained from the current NMR of H. halobium are consistent with: (1) fractional binding of less than 3% of the total intracellular K+, (2) a small ordering factor characterizing all of the intracellular K+, or (3) some combination of the two.