The determination of boron in magnesium oxide using the10B/p, /7Be,10B/d, n/7Be, and10B/d, n/11C reactions is described. Lithium interferes the nuclear reactions leading to beryllium-7. Combination of a proton and deuteron irradiation, each followed by measurement of the induced beryllium-7 activity, allows a simultaneous determination of boron and lithium. The10B/d, n/11C reaction is free from nuclear interferences. The boron concentration ranges from 1.5 to 850 g g–1. The results obtained by the two methods are in good agreement.