Endomyocardial biopsy is the gold standard to diagnose cardiac allograft rejection, although a noninvasive modality such as brain natriuretic peptide (BNP) is attractive. The authors examined the correlation of BNP levels with rejection patterns and allograft function in cardiac allograft recipients followed up to 8 years. One hundred forty-four consecutive patients underwent endomyocardial biopsy, right heart catheterization, and blood sampling. BNP levels decreased during the first 6 months after transplant but then reached a plateau. Time-dependent correlations were made between BNP levels and allograft rejection, left ventricular ejection fraction, pulmonary capillary wedge pressure, right atrial pressure, and serum creatinine. BNP levels were not different between patients with any rejection pattern and no rejection prior to or after 6 months following transplant. BNP levels did not correlate with ejection fraction, pulmonary capillary wedge pressure, right atrial pressure, or creatinine in the first 6 months after transplant. Statistically significant correlations existed between BNP and these parameters after 6 months following transplant. In cardiac transplant recipients, BNP levels decrease in the first 6 months following transplant and then reach a plateau regardless of the presence, type, or severity of allograft rejection. BNP levels do predict allograft rejection but correlate with allograft function after 6 months following transplant.