A technique of low-field pulsed proton nuclear magnetic resonance (NMR) spinrelaxation is described for characterizing the porosity and (effective) poresize distribution in vitro in human compact bone. The technique involvesspin–spin relaxation measurement and inversion spin–spin relaxation spectralanalysis methods. The spin–spin relaxation decay curve is converted into aT2 distribution spectrum by a sum of single exponential decays. The advantages of usinglow-field NMR for the spin–spin relaxation technique are illustrated. The results obtainedfrom NMR methodology are compared with the results obtained from currently availablebut destructive histomorphometry and mercury porosimetry methods. The NMR porositiescorrelate well with the results obtained from the histomorphometry measurements ofeight samples from donors of ages 21–89 years. The pore size distributions fromT2 relaxation measurements are similar to the distributions obtained from the mercuryporosimetry and histomorphometry measurements. This indicates that the age-relatedporosity and pore size changes in human compact bone can be detected using the low-fieldNMR technique.