Helicobacter pylori was grown on solid medium for up to 5 weeks. Morphological conversion from spiral to coccoid forms began after 7 days incubation under microaerophilic conditions. Similar to the exponential cultures, the ageing bacteria produced alkaline phosphatase, acid phosphatase, leucine arylamidase and naphthol-AS-beta 1-phosphohydrolase, although there was a reduction in the levels of the latter two enzymes. Unlike the other enzymes, urease was not detected in 5-week-old cultures. By using primers based on urease subunit C and 26 kD protein genes for polymerase chain reaction (PCR) these two important gene fragments remained conserved despite the morphological conversion from spiral to coccoid forms. Furthermore, PCR-based random amplified polymorphic DNA (RAPD) fingerprinting showed similar DNA banding patterns from bacteria of various ages, demonstrating the conservation of the DNA composition despite morphological changes. This study shows that the aging coccoid form of H. pylori, although reportedly non-culturable in vitro, remains genetically unchanged indicating that it is likely to be viable.