BACKGROUND: Cytological examination is of suboptimal sensitivity but high specificity for the diagnosis of malignant pleural effusions (MPEs). Pleural fluid extracellular vesicles (PFEVs) are enriched with disease-specific microRNAs (miRNAs) which may improve the diagnostic yield for MPE. Our previous study demonstrated the feasibility of isolating miRNAs from PFEVs and profiling PFEV miRNAs by Nanostring nCounter METHODS: Extracellular vesicles (EVs) from pleural fluids were isolated by two sequential ultracentrifugation steps. PFEVs were extracted and characterised by western blotting analysis, particle analysis by tunable resistive pulse sensing (TRPS) technology, and transmission electron microscopy (TEM). Total RNAs (including miRNAs) were extracted from PFEVs and profiled by the Nanostring nCounter RESULTS: EVs from pleural fluids were evident by staining of positive EV-associated protein markers, particle size distribution within the expected parameters, and the cup-shaped morphology by TEM. Employing Nanostring nCounter CONCLUSIONS: The miRNAs identified from this study could be interrogated further for their utility as a single biomarker candidate or to be tested simultaneously in a panel to complement pleural effusion diagnostics. PFEV miRNAs represent a novel bioresource with potential to aid in the diagnosis of pleural effusions. Larger prospective studies are needed to confirm their diagnostic utility.