The addition of Braun and Wood's inorganic supplements (845 mg l−1 KCl, 1800 mgl−1 NaNO3, 300 mg l−1 NaH2PO4.2H2O, 790 mg l−1 (NH4)2SO4) to White's medium caused marked increases in the growth of normal tissues of Helianthus annuus, Nicotiana rustica, Daucus carota, and Vinca rosea and crown-gall tumour tissues of H. annuus. However, no evidence was obtained which suggested that the presence of these extra salts markedly influenced the essential requirements of normal callus for auxins and kinetin. In contrast their presence significantly influenced the hormonal requirements of certain habituated cultures of H. annuus and V. rosea. These habituated cultures had specific auxin requirements on White's medium while either an auxin or kinetin was sufficient on high-salts medium. These results are discussed in relation to previous reports which suggested that the biosyntheses of auxins and other growth factors in normal and crown-gall cultures are specifically activated by certain inorganic ions.