A patient with nephrotic syndrome and morbus Kimura (eosinophilic granuloma) showed chylous ascites. Ascites chylomicrons were analyzed and used to study the substrate specificity of lipoprotein lipase and hepatic triglyceride lipase. Ascites triglyceride and cholesterol concentrations were 191 and 12 mg/dl, respectively. Both apo CII and apo CIII content in ascites were approximately one-third of those of plasma from normal subjects. Ascites chylomicrons were incubated with either lipoprotein lipase or hepatic triglyceride lipase, which were prepared from postheparin plasma using heparin-Sepharose affinity chromatography. Lipoprotein lipase hydrolyzed ascites chylomicrons, while hepatic triglyceride lipase did not. These results suggest different functions of these two lipases in chylomicron catabolism.