The effect of Phytophthora parasitica var. nicotianae (Ppn) race 0 culture filtrate (CF) on direct organogenesis in tobacco stem explants was evaluated using six tobacco cultivars, which were selected based on their field reaction to Ppn. The culture filtrate used in concentrations 5, 10, 15, 20% in MS media suppressed bud formation of stem explants from susceptible tobacco cultivars more than those from resistant tobacco cultivars. This finding indicates that the so-called different level of resistance expressed in the field among tobacco cultivars is expressed in vitro at the stem explants level. The CF from Ppn proves to be very useful in in vitro evaluation of tobacco cultivars for resistance to Ppn and for in vitro selection for disease resistance.