The electrical properties of red blood cell (RBC) suspensions are influenced by flow conditions, and prior studies indicate that electrical properties may reflect the kinetics of RBC aggregation. Changes of conductance and capacitance were monitored and had a time course resembling a "syllectogram" (i.e., temporal change of light reflectance from an RBC suspension after sudden cessation of flow). In the present study, both AC electrical conductance (EC) across and light transmission (LT) through a 1 mm ID glass tube were recorded simultaneously after a sudden stoppage of flow for RBC at various hematocrits in plasma or in isotonic saline (PBS). Preliminary results indicate that EC and LT signals for RBC in plasma have similar time courses, both increasing after an initial decrement of a few seconds duration. Aggregation indexes and aggregation half times calculated using LT and EC showed a similar dependence on hematocrits between 30-50%. Interestingly, RBC in PBS also exhibited a syllectogram time course for conductance, whereas LT continued to decrease after an initial decline reflecting RBC shape recovery. These results suggest that electrical conductance in aggregating and non-aggregating suspensions may be sensitive to phenomena other than RBC aggregation.