11B NMR chemical shifts and linewidths have been measured in very dilute aqueous solutions of boric acid and borates. The results can be explained bv taking pH dependent weighted averages over the species B(OH)3 and B(OH)4−. The11B−10B primary isotope effect on the magnetic shielding is smaller then 3 · 10-8. The H2O - D2O solvent isotope effect on T1 has been established for 11B and 10B in the species mentioned, and from the ratios of T1 the quadrupolar origin of the relaxation mechanism has been inferred.