Alginates are composed of beta-D-mannuronic acid (M) and alpha-L-guluronic acid (G). In this study, block distributions of alginate samples were measured by a chemical fractionation method and H-1-NMR spectroscopy, to compare the usefulness of the two methods. Block distribution results obtained from the two methods were found to be statistically different from each other; the chemical fractionation method gave consistently lower estimates for the amount of homopolymeric blocks. The repeatability of the results was also lower in the chemical fractionation method. By contrast, H-1-NMR spectroscopy was found to be a reproducible and a faster method for determining the distribution of monomeric blocks in alginates.