Fibroblasts are mesenchymal cells which came from the embryonic mesoderm. They are useful for a wide range of cellular and molecular studies as they are one of the easiest types of cells to grow in culture. Their durability also makes them amenable to a variety of manipulations ranging from studies employing gene transfection to microinjection. There is evidence showing that fibroblasts in various organs are intrinsically different. Specifically, human pulmonary artery fibroblasts (HPAF) are important modulators of vascular wall function. During pathological conditions, such as hypoxia-induced pulmonary hypertension, HPAF become proliferative which contributes to adventitial thickening. HPAF play an important role in vascular disease research helping to identify new therapeutic targets to treat pulmonary vascular disease. They are also useful tools to stablish in vitro disease models for High Throughput and High Content Screening.