The role of pleural diaphragmatic lymphatics was studied in twenty anesthetized, paralyzed and mechanically ventilated rats. Lymph formation and propulsion along the network is sustained by transmural and/or intraluminal pressure gradients aided by unidirectional valves. Our previous data show that diaphragmatic lymph flow depends not only on passive pressure gradient related to changes in local tissue stress, but also upon the contractile activity of smooth muscle cells (SMC) within the vessel walls identified by immunofluorescence. Therefore, in order to clarify the structure/function relationship in different tracts, the pleural diaphragmatic lymphatic network was in vivo stained by an intraperitoneal injection of FITC-dextrans. Video recorded images of contracting vessels present in the extreme muscular periphery were collected with a CCD camera for further analyses of the contractile activity and samples of the diaphragmatic contractile vessels and adjacent tissue were used for whole mount immunofluorescence. At least four families of lymphatics vessels were identified: a) not contracting, with discontinuous SMCs layer; b) actively contracting, surrounded by a dense SMCs mesh; c) with an alternate passive/active behavior, and d) with completely passive behaviour with scanty SMCs component. Data suggests that active sites trigger spontaneous contraction waves which sequentially propagate to adjacent segments supporting lymph propulsion along the network.