The exceptionally high capacity for transformation to autotrophy for hormones (habituation) discovered in Nicotiana bigelovii led us to a comparison of the responses of 2 varieties (quadrivalvis and bigelovii) to different hormone treatments applied to their seeds. Hormones used were: kinetin (0.8, 1.6, 3.2 ppm), 2,4-D (0.1, 0.4 ppm), IAA (2 ppm) and NAA (1, 2, 4 ppm). Callus formation and habituation were scored after transfer on minimal medium (without hormones) 3 months after sowing. Var. quadrivalvis showed a much higher ability to form callus but the callus formed was autonomous in a lower percentage of cases when IAA or kinetin treatment was considered. Analysis of auxin-like substances in leaves of the 2 varieties showed a higher content in N. bigelovii var. quadrivalvis. Data are discussed with particular regard to their relevance to tumorous phenomena in plants.