Plasma lipoprotein lipase activity following intravenous injection of heparin or post-heparin lipolytic activity (PHLA), is generally believed to function as a lipemia clearing factor and there have been many reports of studies concerning its changes associated with the progress of atherosclerosis or aging. The findings in my clinical investigation that normal subjects showed PHLA values significantly lower than those in atherosclerosis and that PHLA declined pysiologically with the advancing age prompted me and experimental study in three diet groups of rabbits (vegetables, bean-curd refuse, and lanolin) with the purpose of clarifying the underlying mechanism. 1) Normal subjects showed PHLA values (553.0±125.0μEq/L, N=33) significantly lower than those in atherosclerosis (252.0±41.0μEq/L, N=15, P<0.05) and that PHLA diclined physiologically with advancing age. 2) There was evidence of progressive physiological decline of PHLA over a six-month period of continuous observation in all diet groups of animals. In rabbits with hyperlipidemia maintained on lanolin diet, the fall of PHLA was earlier in onset along with development of lipemia. 3) The pattern of PHLA decline was observed to differ noticeably among the three diet groups. 4) Rabbits fed bean-curd refuse diet and those receiving lanolin diet were sacrificed after six months of observation and histopathologic examinations made of slides prepared from the thoracic and abdominal aorta revealed definite arteriosclerotic changes in lanolin-fed animals but no such microscopic evidence in those fed bean-curd refuse. The lanolin diet group displayed a significantly greater decline of PHLA, as compared with the bean-curd refuse diet group.