Abstract Most of the stress proteins induced after exposure of Zymomonas mobilis to sublethal heat or ethanol shock were shown to be major cellular proteins even in unshocked bacteria. However, a new polypeptide (E 18.5) was detected only after thermal or alcoholic stress. The appearance of E 18.5 was shown to be unrelated to a degradation process but to depend on protein synthesis. Induction of E 18.5 synthesis was controlled at the transcription level and the same conclusion can be drawn for other stress proteins. When cells entered the stationary phase, most of the proteins synthesized were of the stress protein group, including E 18.5. It is suggested that stress proteins, particularly E 18.5, could play an important role in the physiology of Z. mobilis and that they could be directly or indirectly involved in the mechanism of ethanol tolerance.