Abstract.Very low density lipoprotein kinetic parameters were compared in familial hypertriglyceridaemia and familial combined hyperlipidaemia, two distinct genetic forms of hypertriglyceridaemia. Very low density lipoprotein apoprotein B turnover rate was greater in hypertriglyceridaemic subjects with familial combined hyperlipidaemia (0.99 ± 0.27 mg/kg)/h;n= 5;P<0.005) and also in familial hypertriglyceridaemia (0.74 ± 0.10;n= 6;P<0.005) than in age and weight matched non‐hyperlipidaemic controls (0.54 ± 0.21;n= 6), suggesting that the hypertriglyceridaemia seen in both genetic disorders was due to very low density lipoprotein overproduction. Very low density lipoprotein apoprotein B turnover rate was greater in familial combined hyperlipidaemia than in familial hypertriglyceridaemia while plasma triglyceride turnover was higher in familial hypertriglyceridaemia. This disparity in the turnover rates of apoprotein B and triglyceride between these disorders was accompanied by a higher very low density lipoprotein triglyceride/apoprotein B ratio in familial hypertriglyceridaemia than in familial combined hyperlipidaemia (P<0.001) and in normals (P<0.005).The findings suggest that the hypertriglyceridaemia of familial combined hyperlipidaemia is due to overproduction of very low density lipoprotein of normal composition, while that of familial hypertriglyceridaemia is due to oversecretion of triglyceride‐enriched very low density lipop