11B NMR spectra of the reaction products present in solutions of boric acid and protein such as albumin were done to determine the boron species present in protein borate wood preservatives. At acid pHs only the undissociated H3BO3 at 20 ppm occurs, while at alkaline pH the signals of the charged and uncharged boron atoms at 16 ppm and 12.6-13.7 ppm of the three ionic species [B(OH)4]-, [B303(OH)4]-, [B303(OH)5]2- occur. A third much smaller intensity signal at 1.7-1.8 ppm due to the reaction of a polyborate compound with the protein is also present. Application of heat causes a relative increase in the proportion of the latter two signals indicating both an increase of charged structures in solution and of the proportion of boron ions having reacted with the protein, the higher temperature having increased its solubility. This is compared and related to the effectiveness of albumin borate at different pHs and in relation to the different extent of leaching of boron species in both laboratory and field trial experiments. Both laboratory and field trials are reported. This is also related to previous findings as regards the effectiveness of proteins of different isoelectric point when used in protein borates wood preservatives, and to the influence of pH on the performance of these wood preservatives.