Brain natriuretic peptide is proposed as a biochemical marker which could provide a useful screening test to select patients for further cardiac investigations in heart failure. The applicability of such a biochemical test in clinics, hospital wards, and clinical laboratories is dependent on its ease of use and on the complexity of sample handling. The present study was undertaken to evaluate the stability of brain natriuretic peptide under a number of different handling conditions (sample collection, storage temperatures, freezing temperatures) assayed with a commercially available kit. The results clearly demonstrate that brain natriuretic peptide is stable at room temperature for 24 hours, or in up to 30 degrees C for 12 hours in the presence and absence of aprotinin, on the condition that brain natriuretic peptide is assayed within one month (frozen at -20 degrees C) after blood collection. The presence of aprotinin prevents brain natriuretic peptide degradation in samples preserved for more than 1 month at -20 degrees C before assay.