Bacterial evolution and genetic exchange. Genetic bases for evolutionary development in microorganisms (W. Arber). Horizontal genetical exchange in the evolution of Neisseria meningitidis outer membrane proteins (M.C.J. Maiden, J. Suker, I.M. Feavers). Ecology and infection mechanisms of pathogenic Neisseria species (T.F. Meyer). Analysis of a genetic event associated with the birth of the current cholera epidemic in Asia (F.R. Mooi, E.M. Bik, A.E. Bunschoten). Genetic diversity in uropathogenic Escherichia coli as shown by RAPD (F. Rodriguez-Valera et al ). 16S rRNA hybridization probes for the major groups in intestinal bacteria: development in in situ application (F. Schut). Applications in ribosomal in situ hybridization for the study of bacterial cells in the mouse intestine (T.R. Licht et al). Host parasite interactions. Bacterial resistance to macrophage killing. An evolutionary perspective (A.E. Hromockyj, S. Falkow). Molecular cross talk between bacteria and their hosts (A. Camilli et al). Biology of aphid endosymbionts (Genus Buchnera) (P. Baumann). Pathogenicity of Yersinia: A strategy for extracellular survival and multiplication (J. Heesemann et al). Molecular and cellular bases of invasion of the intestinal mucosa by Shigella flexneri (P.J. Sansonetti). Repetitive DNA as a tool to study the genetic variation and epidemiology of Mycobacterium tuberculosis (J.D.A. van Embden). Macrophage-induced genes of Salmonella Typhimurium (J.G. Kusters et al). Population genetics and clonal spread Recombination and DNA sequence variation in E coli (R. Milkman). DNA sequence analysis of the genetic structure and evolution of Salmonella enterica (R.K. Selander). Spread of serogroup A meningococci: a paradigm for bacterial microevolution (M. Achtman). Evolution of penicillin-binding protein genes of sensitive Streptococci into resistance determinants of streptococcus pneumoniae (R. Hakenbeck). Specialized clones and lateral transfer in pathogens (P. Reeves). Pathogenic bacteria: the wisdom of their genes (E.R. Moxon, P.B. Rainey). Posters.