Lipoprotein lipase (LPL) activities in parametrial and interscapular adipose tissue, soleus and adductor longus muscles and hearts of female rats were measured during progressive starvation, chow re-feeding after 24 h starvation and throughout dark and light phases in rats permitted unrestricted access to chow. Adipose-tissue LPL activities declined by 50% after 6 h starvation and continued to fall as the starvation period was extended to 24 h. Skeletal-muscle LPL activities dramatically increased between 9 and 12 h of starvation. Cardiac LPL activities increased 2.5-fold within 6 h of starvation, reaching a maximum after 12 h of starvation. Adipose-tissue LPL activities increased rapidly within 2 h of re-feeding chow ad libitum after 24 h starvation, achieving 'fed ad libitum' values after 6 h. Oxidative-skeletal-muscle LPL activities also increased after 2 h of refeeding and exceeded 'fed ad libitum' values throughout the 6 h re-feeding period. Cardiac LPL activities remained up-regulated for the 6 h of re-feeding. Adipose-tissue LPL activities exceeded those of cardiac or skeletal muscle throughout both light and dark phases. The lowest adipose-tissue LPL activities were observed at 9 h into the light phase. In contrast, cardiac LPL activity declined throughout the dark phase, with a minimum at 9 h into the dark phase. No such variation was observed for skeletal-muscle LPL activities. A diurnal nadir in plasma triacylglycerol (TG) concentrations coincided with the peak in cardiac LPL activities. The results demonstrate that, during unrestricted feeding and re-feeding after prolonged starvation, changes in skeletal-muscle and adipose-tissue LPL activities are neither reciprocal nor co-ordinate. Regulation of cardiac LPL activity during the diurnal cycle may be an important aspect of both of cardiac fuel selection and whole-body TG metabolism.