After cardiac transplantation clinicians want to prevent allograft rejection while minimizing immunosuppressive side effects. The gold standard of rejection monitoring in cardiac transplantation is endomyocardial biopsy (EMB). However, EMB is invasive, expensive, subject to sampling error, inter-observer variability, and causes morbidity (0.5–1.5%). Also, EMB cannot be done as frequently as the clinicians may want so there is a critical need to be able to do a non-invasive blood test which can help inform the clinician about the state of the allograft. This talk is about development of a gene expression signature from PBMC which reflects the state of (rejection or no-rejection) status of the allograft from PBMC using real time PCR for multiple genes and pathways to detects the absence of moderate/severe acute cellular cardiac allograft rejection (ISHLT grade =3A) thus potentially reducing the frequency of graft biopsy in certain clinical settings. For development of gene signature, data from 252 real-time PCR assays on 145samples were used to train the algorithm. This gene signature included 11 genes and was validated on unique samples in a prospective and blinded manner. The gene signature distinguished moderate/severe rejection from quiescence (t-test, p=0.0018).