We thank very much Dr. Souza et al for their interest in our article (May 2006)1on the potential clinical role of N-terminal-pro-brain natriuretic peptide (NT-proBNP) estimation in patients with pulmonary arterial hypertension (PAH). We also agree with their concerns regarding the universal validity of the prognostic cutoff values that were reported in our article. Clearly, with a study group of slightly > 50 patients we would not impose or recommend such values for universal prognostic use. Furthermore, we do not believe that even the most sophisticated statistical analysis could extract more objective truth from such a database. On the other hand, by looking at the receiving operating characteristic analysis and trying to identify prognostic thresholds we wanted to avoid the common practice of reporting the prognostic significance of median values. While highly dependent on the initial characteristics of the study group of the index trial, such median values later often become surprisingly “magic numbers” and are extrapolated to other populations with even less evidence. This was the case both for a 6-min walk test distance of 332 m or an NT-proBNP concentration of 150 pg/L as a result of the reports of Nagaya et al2and Miyamoto et al.3Therefore, rather than defending our 1,400 and 3,400 pg/L thresholds, even though they were derived from a receiving operating characteristic analysis, we would reply by issuing a call for pulling together data on PAH patients whose baseline clinical characteristics and NT-proBNP concentrations were tested with a method similar to the one used in our study. This may be true, for instance, for the study population of a trial recently published by Souza et al.4 We have recently witnessed a great step forward in the understanding of the efficacy of the new drugs developed for the treatment of PAH thanks to global collaboration between expert centers. It is time to try to start building networks of collaboration to learn more about prognostic indexes and clinical end points. We would be available for this type of collaboration.