Weintroducethenotionofproperty（RD）foralocallycompact,Hausdorffandr-discretegroupoidG,andshowthatthesetS2^l（G）ofrapidlydecreasingfunctionsonGwithrespecttoacontinuouslengthfunctionIisadensespectralinvariantandFreehet＊-subalgebraofthereducedgroupoidC^＊-algebraCr^＊.（G）ofGwhenGhasproperty（RD）withrespecttol,sotheK-theoriesofbothalgebrasareisomorphicunderinclusion.EachnormalizedcoeycleconG,togetherwithaninvariantprobabilitymeasureontheunitspaceGoofG,givesrisetoacanonicalmapTconthealgebraCo（G）ofcomplexcontinuousfunctionswithcompactsupportonG.WeshowthatthemapTccanbeextendedcontinuouslytoS2^l（G）andplaysthesameroleasann-traceonCr^＊（G）whenGhasproperty（RD）andcisofpolynomialgrowthwithrespecttol,sotheConnes＇fundamentparingbetweentheK-theoryandthecycliccohomologygivesustheK-theoryinvariantsonCr^＊（G）.
