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Fifty-five Precambrian ultramafic to felsic granulites from Pikwitonei, Westport, Adirondack Mountains, Orissa, Madras, and Minnesota and granulite xenoliths from Montana have been analyzed by Prompt Gamma Neutron Activation Analysis and alpha-track mapping. Boron contents vary between <0.1 and 14 ppm, except for 3 rocks containing >100 ppm, and do not show any relationship to other major or trace elements. The B abundance is proportional to the abundance of hydrous alteration products (sericite, saussurite, chlorite) which contain up to 500 ppm, in a given rock. Boron also is concentrated in some cases in mineral cleavages, along grain boundaries and along rock fractures: in some samples it is localised at points within plagioclase grains which might represent fluid inclusions. The rock-forming minerals also contain a little homogeneously distributed B, with abundance decreasing from: biotite > clinopyroxene > orthopyroxene, amphibole, plagioclase > perthite, quartz. The average abundance of B in the lower continental crust may be approximated by the average granulite. With a weighting of 54 : 13 : 31 : 2 for silicic : intermediate : basic : anorthosite + sedimentary gneiss, the lower crust averages 9.3 ppm, close to our 9.2 ppm average for the upper crust. If samples which show a anomalously high alteration of plagioclase are eliminated, the lower crust averages only 2.8 ppm: this latter figure is more representative of fresh lower crustal material.