Slices of Mangifera zeylandica and Hevea brasiliensis wood were impregnated with boric acid (boric acid equivalent: BAE) at various concentrations, and C. <i>domesticus nymphs were cultivated on the slices by a method described previously. The approximate threshold concentrations of BAE in wood were 0.8% for direct toxicity to the termites, and 0.12% for toxicity to the gut fauna. Suggests that 0. 15% would be a suitable concentration for protective purposes. -- AATA