B-type natriuretic peptide (BNP; Abbott Diagnostics) and N-terminal proBNP (NT-proBNP, Roche Diagnostics) were compared in consecutive samples of 458 patients (mean age 60 years+/-16 years; 159 female, 299 male) sent for NT-proBNP measurement to investigate influences on both markers. BNP and NT-proBNP showed a close correlation with each other (r=0.89, p<0.0001). Using age- and gender-adjusted upper reference values the inter-rater agreement of both parameters was satisfactory (83%, Cohen's kappa coefficient=0.7). The combination of normal BNP and elevated NT-proBNP was significantly more frequent than vice versa (61 vs. 16 patients), and a calculated glomerular filtration rate<60 ml/min/1.73 m(2) was found in 39% of these patients. Multiple linear regression analysis revealed a significant influence of a reduced ejection fraction (<50%), renal dysfunction (calculated glomerular filtration rate<60 ml/min/1.73 m(2)), anemia, hypertension, age, and gender on both BNP and NT-proBNP. In conclusion, despite a close correlation and a satisfactory agreement between both markers in classification, frequent discrepancies in individual patients demonstrate that both markers are clinically not completely equivalent.