The study by Weber et al. investigates the distribution and potential biomarker value of microRNAs (miRNAs) in 12 human body fluids, including plasma, saliva, tears, urine, amniotic fluid, colostrum, breast milk, bronchial lavage, cerebrospinal fluid, peritoneal fluid, pleural fluid, and seminal fluid. The researchers used quantitative PCR to survey the miRNA composition in these fluids. Key findings include: 1. **Presence of miRNAs in All Fluids**: MiRNAs were detected in all tested body fluids, with distinct compositions in different types. 2. **Fluid-Specific miRNAs**: Some miRNAs were highly abundant across multiple fluid types, while others were enriched in specific fluids. 3. **Urothelial Cancer Biomarkers**: Urine samples from patients with urothelial cancers showed distinct miRNA patterns compared to normal urine and pregnant urine samples, suggesting potential use of miRNAs as biomarkers for urothelial conditions. 4. **Clustering Analysis**: Unsupervised hierarchical clustering revealed two major groups of miRNA profiles, with plasma clustering separately from other fluids. 5. **miRNA Concentration Variations**: Total RNA and miRNA concentrations varied among different body fluids, with cerebrospinal fluid, tears, and urine containing less RNA than breast milk and seminal fluid. 6. **miRNA Clusters and Tissue Relevance**: Some miRNAs were uniquely present in specific fluid types or tissues, indicating their functional roles or origins. The study highlights the potential of extracellular miRNAs as noninvasive biomarkers for various physiological and pathological conditions, particularly in urothelial cancers.The study by Weber et al. investigates the distribution and potential biomarker value of microRNAs (miRNAs) in 12 human body fluids, including plasma, saliva, tears, urine, amniotic fluid, colostrum, breast milk, bronchial lavage, cerebrospinal fluid, peritoneal fluid, pleural fluid, and seminal fluid. The researchers used quantitative PCR to survey the miRNA composition in these fluids. Key findings include: 1. **Presence of miRNAs in All Fluids**: MiRNAs were detected in all tested body fluids, with distinct compositions in different types. 2. **Fluid-Specific miRNAs**: Some miRNAs were highly abundant across multiple fluid types, while others were enriched in specific fluids. 3. **Urothelial Cancer Biomarkers**: Urine samples from patients with urothelial cancers showed distinct miRNA patterns compared to normal urine and pregnant urine samples, suggesting potential use of miRNAs as biomarkers for urothelial conditions. 4. **Clustering Analysis**: Unsupervised hierarchical clustering revealed two major groups of miRNA profiles, with plasma clustering separately from other fluids. 5. **miRNA Concentration Variations**: Total RNA and miRNA concentrations varied among different body fluids, with cerebrospinal fluid, tears, and urine containing less RNA than breast milk and seminal fluid. 6. **miRNA Clusters and Tissue Relevance**: Some miRNAs were uniquely present in specific fluid types or tissues, indicating their functional roles or origins. The study highlights the potential of extracellular miRNAs as noninvasive biomarkers for various physiological and pathological conditions, particularly in urothelial cancers.