The catalytic rate of membrane-supported lipoprotein lipase has been determined for chylomicron and very low density lipoprotein substrates during the formation of triglyceride-depleted ("remnant") particles. Both lipoprotein species and their generated remnant products were competitive substrates for lipase activity. Remnant formation from each species was associated with decreasing kc but an unchanged apparent Km. This finding was confirmed from the rate of plot of total triglyceride catabolism by lipase at low substrate concentrations. When compared with the major very low density lipoprotein fraction (Sf 100-400), a fraction isolated from plasma with a lower flotation rate (Sf 40-100) had a lipid composition and decreased kc compatible with this representing a physiological remnant particle.