It is an open question whether the coccoid form of Helicobacter pylori is alive in the dormant state or is degenerative and in the process of cell death. We studied the viability of the coccoid form of H. pylori to explore the possibility of infectivity to the host by evaluating its protein synthesis and acid response. Coccoid H. pylori conserved the capability to produce proteins for at least 100 days when stored at 4 degrees C in either phosphate-buffered saline (PBS) or distilled water. After 20 days of storage in distilled water exposure of the coccoids obtained to acidic pH induced expression of the several proteins but inhibited those induced after 20 days of storage in PBS. However, after extending the incubation of the coccoid forms in PBS up to 100 days, the organisms acquired the ability to induce the proteins in response to acid stress. The induction of protein expression may be involved in the biological event of transformation into the spiral form. Furthermore, this altered response of the coccoids to acid shock may determine the potential for morphological reversion during incubation.