Helicobacter pylori has been successfully maintained in a continuous culture system. The culture was grown in 0.6 litre of brain heart infusion broth with supplements in a 1 litre fermenter with a flow rate of 25 ml/h, an 80% dilution rate and a specific growth rate of 0.06/h. Unlike the typical growth curve which occurred in batch culture, the growth pattern in continuous culture showed a short lag phase following which growth was maintained in exponential phase with > or = 10-fold increase in viability and the pH was stabilised at 6.95 +/- 0.05. The urease activity remained constant in relation to viability while the urea was completely hydrolysed. The system provides cells with growth characteristics similar to the fresh isolate which are highly adaptable to the in vitro environment. This study shows that continuous culture is a simple and efficient growth system for the cultivation of a 'synchronous' spiral form of H. pylori.