For many years the study of Red Blood Cell (RBC) deformability has been limited to specialised hematological research institutes and this has hampered a widespread clinical testing of this dynamic RBC property. Consequently, the clinical relevance of such in vitro measurements has remained questionable now for a considerable time. The recent availability of the LORCA, a routinely applicable and computer assisted instrument for this purpose, opens now the possibility to evaluate RBC deformability on a large scale in various pathological situations associated with impaired microcirculatory flow. In this communication we present our clinical experience obtained thusfar with this instrument. Besides the effect of physiological aging of normal RBC, the results of a clinical study on malaria tropica, case studies of hereditary elliptocytosis, Smith-Lemli-Opitz syndrome (a cholesterol biosynthesis defect), the treatment of sickle cell crisis with hydroxy-urea as well as the clinical intervention with Cyclosporin, are collected. In conclusion, it can be stated that the limited clinical experience with the LORCA as is reported here, yields sufficient evidence about the clinical potential of this technique.