The present study examined the levels of NMDA receptor NR2 subunit tyrosine phosphorylation in a rat model of inflammation and correlated it with the development of inflammation and hyperalgesia. Hindpaw inflammation and hyperalgesia were induced by intraplantar injection of complete Freund's adjuvant. Proteins from the spinal cord (L4-L5) were immunoprecipitated with anti-NR2A or anti-NR2B antibodies and used for subsequent analysis using 4G-10, a specific anti-phosphotyrosine antibody. Compared with naive rats, there was a rapid and prolonged increase in tyrosine phosphorylation of the NR2B, but not NR2A, subunit after inflammation. The increase in NR2B tyrosine phosphorylation was dependent on primary afferent drive because (1) the phosphorylation correlated with the temporal profile of inflammation and hyperalgesia, (2) shorter-duration noxious stimulation produced a rapid and shorter-lasting increase in phosphorylation, and (3) local anesthetic block of the injected paw reversibly blocked inflammation-induced NR2B tyrosine phosphorylation and delayed hyperalgesia. The increase in NR2B tyrosine phosphorylation was abolished by intrathecal pretreatment with genistein, a tyrosine kinase inhibitor; PP2, an Src family tyrosine kinase inhibitor; AIDA, a group I metabotropic glutamate receptor antagonist; L733,060, an NK1 tachykinin receptor antagonist, and chelerythrine, a protein kinase C inhibitor. In addition, intrathecal PP2 delayed the onset of mechanical hyperalgesia and allodynia. These findings correlate in vivo NMDA receptor tyrosine phosphorylation with the development and maintenance of inflammatory hyperalgesia and suggest that signal transduction upstream to NR2B tyrosine phosphorylation involves G-protein-coupled receptors and PKC and Src family protein tyrosine kinases.