The interaction between Yersinia and animal cells has become one of the major paradigms in understanding microbial pathogenicity. There have been numerous advances in our understanding of Yersinia-mammalian cell interactions within the past year. A process of virulence protein regulation and export has been studied in more detail, an alternative pathway for cellular attachment and entry has been defined, and some insight has been gained into how these determinants disrupt normal host cell signal transduction mechanisms coincident with bacterial attachment and cellular entry. The biochemical interplay during infection provides information about bacterial strategies for growth and survival, as well as insight into normal eukaryotic cell function.