<p>Micro- and nanoplastics are an increasing focus in biomedical research, yet their definition, classification, and detection methods remain largely unstandardised. The lack of consistent nomenclature, agreed size criteria, and uniform reporting methods significantly hinders comparison of available data. Therefore, a systematic review of studies on analytical methods for detecting micro- and nanoplastics ex vivo in human biological samples was conducted. Most included studies (63.89%) were published between 2024 and 2025, highlighting the topicality of this research area. Study populations varied widely in age and health status, and sample sizes were often small. The most frequently analysed samples included placenta, kidneys, liver, lungs, heart, and urine, while other tissues were reported sporadically. Detection methods primarily involved microscopic techniques, chromatographic approaches, and Raman and FTIR spectroscopy. Considerable variability was observed in sample preparation procedures, including storage, digestion, and filtration, which may affect analytical sensitivity and specificity. Differences were also noted in quality control strategies and contamination minimisation approaches. Reported particle sizes and concentration units varied substantially, and many studies did not distinguish between microplastics and nanoplastics, treating them as a single category. This further hinders data comparison and the accurate assessment of human exposure.</p>