Transformation-induced slow growth phenotype (SGP) in yeast is repressed in the presence of 2 mu m plasmids. A full 2 mu m-sequence-based recombinant plasmid (pJB502) was found to be more stable in a 2 mu m-free- [cir(o)] strain of Saccharomyces cerevisiae than in a cir(+) strain. This could not be attributed to differences in growth rate calculated from kinetic analysis of plasmid loss, but transformed [cir(o)] isolates, which had lost the recombinant plasmid, exhibited varying degrees of SGP in batch culture. One of these isolates was outcompeted in chemostat culture by the recombinant-plasmid-containing strain, suggesting that improved plasmid maintenance can result from SGP in cir(o) hosts.