Lilium pomponium and Lilium martagon belong to the Liliaceae family and in Italy are submitted to a total protection by regional laws in Liguria and Piedmont. The ornamental value of these species is high and they are also used for breeding programs to obtain commercial cultivars. The micropropagation provides an adequate number of plants to be used as mother stock plants and to be re-introduced into the natural habitat. The size of the bulbs coming from in vitro culture is a crucial point to guarantee the good acclimatization of the plants and a suitable aerial part development after transfer to soil. The research was conducted to improve the in vitro growth of bulbs in number and dimensions useful for fast re-introduction. Experiments were carried out to evaluate factors typically conditioning bulb development and enlargement, such as medium salt composition, concentration of indole butyric acid, sucrose, photoperiod and temperature. For L. martagon, the multiplication rate, in term of bulb/explant, is best obtained with the use of WPM salts, with a temperature of 18°C and a sucrose concentration of 30 g/L; L. pomponium propagated better in the presence of MS salts supplemented with 30 g/L of sucrose and 0.5 mg/L of IBA, at 24°C with a photoperiod of 16 hours of light. Results show that in order to obtain large bulbs is preferable to use salts, at a temperature of 24°C, with high IBA and sucrose concentration. The in vitro growth in darkness in L. pomponium ensures higher bulbs weight; after 6 months of ex vitro growth, it was possible to obtain a minimum of 57% to a maximum of 84.5% of plant survival, in a very good growth conditions.