Aims: Ultrastructural and molecular studies to support the hypothesis of programmed cell death in Helicobacter pylori were conducted. Methods and Results: Evidence of programmed death in H. pylori is provided through electron microscopic detection and cytochemical labelling of electrondense bodies (EDB), containing packaged DNA in coccoid cells, resembling micronuclei of apoptotic eukaryotic cells. This morphological evidence is also supported by DNA cleavage in homogeneous fragments of about 100 base pairs. Programmed cell death was observed in H. pylori cultures at 37 degreesC, with a maximum of 37.5% of EDB coccoid cells after 7 days. The non-permissive temperature of 4 degreesC anticipated this process, with 40% of EDB coccoid forms within 3 days, and it remained substantially unaffected during the observation time of 14 days. Conclusion: In these experiments, deprivation of nutrients and a non-permissive temperature acted as a powerful trigger for programmed cell death. Significance and Impact of the Study: Helicobacter pylori bacterial populations, under stressing stimuli, can respond with programmed cell suicide as a means of species preservation.