the purpose o f this study was to investigate the effects o f acute eccentric exercise on heat shock protein (hsp) 72 expression, and the relationships between hsp72 levels with age, doms, and type i myosin heavy chain (mhc) protein levels in skeletal muscle o f young and older men. seven older (60.9 ± 0.8 years) (mean ± se) and nine young (23.1 ± 1.1 years) healthy, moderately active males performed five sets o f one legged eccentric exercise. the intensity o f the first four sets were 60, 66, 72, and 84% o f the subjects’ pre-determined concentric 10-rm (repetition maximum) with 10 repetitions in each set. the subjects exercised to fatigue at 120% o f the 10- rm cone for the last set. muscle biopsies were obtained from the vastus lateralis muscle one week prior to the exercise from the contralateral leg, and 30 minutes, 24 hours and 72 hours after the exercise from the exercised leg. subjects reported doms (delayed-onset muscle soreness) at the time of each muscle biopsy from a questionnaire. muscle tissues were analysed by sds-page and western blotting. there was no difference in hsp72 levels before and after exercise, nor was there difference in the two subject groups at any o f the time points. there was significant difference in doms before and after exercise (p < 0.001 ) but no difference between the young and the older subjects. there was no correlation between hsp72 content and age, doms, or type i mhc contents. based on these findings, it seems that the nature and the volume o f exercise may be partly responsible for hsp72 expression in human skeletal muscle. more studies are needed in examining the relationship between hsp72 content and doms and type i mhc levels in human skeletal muscle.