['The ability to deform is important for circulating RBCs in vivo, and earlier studies showed that this property can objectively be measured in vitro by the LORCA. In this study it was investigated whether photodynamic treatment of human RBCs (meant to inactivate contaminating pathogens) affects deformability.', 'WBC-reduced RBC suspensions (30% Hct) were treated with 1,9-dimethylmethylene blue (DMMB) and red light. Changes in deformability were analyzed by LORCA measurements, in which elongation of the cells is measured at increasing shear stress. The effect of DMMB concentration and light dose was determined as well as the interfering effect of two scavengers of reactive oxygen species, that is, dipyridamole and Trolox.', 'Photodynamic treatment with DMMB resulted in clear changes in RBC deformability. Deformability changes occurred before onset of hemolysis. Under relatively mild treatment conditions, especially deformability at low shear stress was decreased, whereas deformability changes at high shear stress only occurred under harsher treatment conditions. Inclusion of dipyridamole and/or Trolox primarily prevented deformability changes at high shear stress.'] Do laser-assisted optical rotational cell analyzer measurements reveal early changes in human RBC deformability induced by photodynamic treatment?