Tyrosine phosphorylation is a critical regulator of bacterial virulence, with the associated protein tyrosine phosphatases (PTPs) and bacterial tyrosine kinases (BY-kinases) recognised as major virulence factors in a range of bacterial pathogens including Streptococcus pneumoniae. For some time we have been interested in a tyrosine phosphoregulon in the pneumococcus comprising of CpsB (a PTP) and CpsC and CpsD, which together form an active BY-kinase. This system plays a crucial role in the regulation of capsule biosynthesis. While homology searches did not uncover additional BY-kinases, the protein encoded by one open reading frame (designated PTP) shows homology to the low molecular weight protein tyrosine phosphatases, which play a role in capsule regulation in other bacteria, as well as diverse roles including responding to stress, and biofilm formation. Thus, we set out to investigate what roles this plays in the pneumococcus. Purification of the PTP from E. coli, enabled us to show that PTP is indeed a phosphatase, with specificity against tyrosine. We have also constructed mutations on the chromosome of the pneumococcus which has shown that the PTP does not play a role in the regulation of capsule. This suggests that the phosphatase may have other roles, and that tyrosine phosphorylation has wider reach of affects in the pneumococcus than solely capsule biosynthesis.