1. Quantitative reverse transcriptase polymerase chain reaction (RT–PCR) analysis has previously shown that the P2Y(14) receptor is expressed in peripheral immune cells including lymphocytes. Although in transfected cells the P2Y(14) receptor couples to pertussis toxin-sensitive G(i/o) protein, the functional coupling of endogenously expressed P2Y(14) receptors to the inhibition of adenylyl cyclase activity has not been reported. Therefore, the primary aim of this study was to determine whether the P2Y(14) receptor is functionally expressed in murine spleen-derived T- and B-lymphocyte-enriched populations. 2. RT–PCR analysis detected the expression of P2Y(14) receptor mRNA in whole spleen and isolated T- and B-lymphocytes. 3. In T cells, UDP-glucose (EC(50)=335 nM) induced a small but significant inhibition (circa 20%) of forskolin-stimulated cAMP accumulation, suggesting functional coupling of endogenously expressed P2Y(14) receptors to the inhibition of adenylyl cyclase activity. In contrast, the other putative P2Y(14) receptor agonists UDP-galactose, UDP-glucuronic acid and UDP-N-acetylglucosamine had no significant effect alone but behaved as partial agonists by blocking UDP-glucose responses. In B cells, UDP-glucose (100 μM) had no significant effect on forskolin-stimulated cAMP accumulation. 4. Treatment of T cells with pertussis toxin (G(i/o) blocker) abolished the inhibitory effects of UDP-glucose on forskolin-stimulated cAMP accumulation. 5. T-cell proliferation in response to anti-CD3 monoclonal antibody (1 μg ml(−1)) was significantly inhibited by UDP-glucose (59% inhibition; p[IC(50)]=5.9±0.3), UDP-N-acetylglucosamine (37%; 6.1±0.3), UDP-galactose (56%; 8.2±0.2) and UDP-glucuronic acid (49%; 6.3±0.2). Interleukin-2- (5 ng ml(−1)) induced T-cell proliferation was also significantly inhibited by all four agonists. 6. In summary, we have shown that the P2Y(14) receptor appears to be functionally expressed in murine spleen-derived T-lymphocytes. These observations suggest that UDP-glucose and related sugar nucleotides presumably via the P2Y(14) receptor may play an important role in modulating immune function.