The pSG5-derived vector plasmids pGM4, pGM9 and pGM12 as well as the plJ101 derivatives plJ303 and plJ702 are stably inherited at non-selective conditions in N-limited chemostats of S. lividans 66. In glucose-limited chemostats only pGM12 and the shuttle vector pGM120 which carry the minus origin of replication are stably maintained. Small vectors lacking the minus origin as pGM4, pGM9, pGM11 and the shuttle vectors pGM103 and pGM160 were lost from the host strain.