Several hydrolytic enzymes and pro-oxidative agents, present in the arterial intima, cause proteolytic, lipolytic and oxidative modifications of low-density lipoprotein (LDL) particles that can result in aggregation and/or fusion of the modified LDL particles[l].In this work the applicability of electrochromatography with open tubular capillaries coated with human low-density lipoprotein (LDL) particles[2] or native lipid droplets to in situ enzymatic modification was studied.LDLs and lipid microemulsions immobilized on the fused silica capillary wall were exposed to sphingomyelinase, phospholipase A2 and-chymotrypsin at ambient and physiological temperatures.The changes in electroosmotic flow mobility as a function of time and temperature of enzymatic treatment were used as an indicator of changes in LDL surface charges, and retention factors of steroids provided information on hydrophobic interactions.