The activation energy of deep traps was studied in a series of beta-rhombohedral boron samples taken from different companies and labs. The presence of deep traps in some samples induces polarization effects in transient photoconductivity experiments. The activation energy of these deep traps, determined by thermally stimulated depolarization-current measurements, is (0.45 ± 0.03) eV in agreement with results previously obtained by other authors using various techniques. The apparent absence of these deep traps in some samples shows that they are not associated. with the complex lattice structure of beta-rhombohedral boron, as suggested by some authors.