Plantlets of lily regenerated in vitro from scale explants consist of scales and leaves from which the base of the petiole has swollen to a scale. Fluridone, an inhibitor of ABA‐synthesis, applied during culture in vitro, inhibited the swelling of the petioles and promoted leaf formation. At high fluridone concentrations (10 or 33μM), swelling was completely blocked, and plantlets consisted of leaves only. Addition of ABA during the regeneration in vitro had the opposite effect and resulted in plantlets with scales only. When applied simultaneously with fluridone, ABA nullified the effect of fluridone. This demonstrates that bulb formation in lily is under the control of ABA. Lily plantlets regenerated in vitro on scale explants at 20 or 25°C were harvested after 11 weeks, and the leaves were removed from the bulblets. The bulblets were dormant and required a cold treatment to achieve rapid emergence after planting in soil. Fluridone added during the culture in vitro prevented the development of dormancy, and the bulblets did not require a cold treatment. The effect of fluridone was nullified by simultaneous addition of ABA. Bulblets harvested after 6 weeks of culture at 20°C had not yet developed dormancy. Bulblets regenerated at 15°C were only slightly dormant. In both types of bulblets, it is unlikely that the lack of dormancy was due to low ABA‐levels since addition of ABA did not affect the dormancy status. These data indicate that the level of endogenous ABA and an unknown additional factor play major roles in the development of d