Antigen K88, one active component of a vaccine against swine colibacillosis, has been cloned and expressed in Escherichia coli strain BB4. This work shows the process of K88 fermentation that yields 151.4 mg/l of K88 at 0.2 vvm airflow and agitation speed of 400 rpm in a 5 1 bioreactor. Scale up to 50 1 was carried out following a constant volumetric oxygen transfer coefficient (K(L)a) criteria and volumetric airflow ratio per unit of volume. (C) 2003 Elsevier Science Ltd. All rights reserved.