1) Aiming at detecting of conformational and/or net charge changes at the microsome surface upon initiation of fusion, predicted on the basis of literature reports of protein alterations, rat liver microsomes were fractionated by capillary electrophoresis in polymer solutions serving as media for """"""""particle sieving"""""""" (separation based on size and shape differences). In non-borate buffer containing optimally resolving polymers, the purified microsome preparation appeared homogeneous. The size of the microsome was estimated in those media as 16 +/- 6 nm geometric mean radius. Upon addition of Mg++ and either GTP-gamma-S (no fusion) or GTP (fusion), several new microsome components are separated. However, their sizes and net charges are not measurable by capillary electrophoresis since they remain unretarded in the water soluble range of available polymers, consistent with the behavior of very large particles. 2) Cisplatin treatment of cells results in a shift from large molecular weight DNA populations to smaller ones. In an attempt to monitor that shift for the purpose of predicting the success of clinical cisplatin treatment, an electrophoretic method for distinguishing DNA populations differing in size was developed, using thymus DNA sonicated for various times as models for such populations.