Predicted lipoprotein genes are over-represented in mycoplasma genomes, suggesting their products play a major role in normal cellular function. Mycoplasma lipoproteins are generally predicted to be exposed to the external milieu and to be tethered to the single limiting cytoplasmic membrane by their amino terminal acyl groups. Thus they are likely to be directly involved in interactions between pathogenic mycoplasmas and their hosts. However, the functions of most of these lipoproteins are yet to be defined. Many lipoprotein genes appear to be members of operons that include predicted transporter genes, suggesting that they may play a role in capture of nutrients from their hosts. We have focussed on defining the biochemical function of a number of mycoplasma lipoproteins, as well as examining the role of specific lipoproteins, or the operons that contain them, in virulence. Our studies have suggested that a virulence gene, mslA, that is conserved in many pathogenic mycoplasmas encodes an oligonucleotide binding lipoprotein, suggesting that the operon that contains it, which also encodes a lipoprotein nuclease, may function in the transport of nucleotides into the cell. We have also demonstrated that the lipoprotein that acts as a substrate binding protein for the oligopeptide transporter plays a significant role in virulence, shown that the putative sugar (or sn-glycerol-3-phosphate) permease, MalF (or UgpA), is essential for survival in vivo, and characterised a lipoprotein lipase that induces growth inhbitory antibody in several pathogenic mycoplasmas. These studies are gradually defining the function of these critical surface exposed proteins of mycoplasmas and their role in the virulence of these important pathogens.