Plasma aspirin esterase activity, expressed as nmol salicylate formed/ml plasma/min, was found to be similar in a group of healthy elderly adults, a group of young adults and a group of frail young adults, but was lower in a sample of frail elderly subjects. This was associated with reduced plasma albumin levels in healthy elderly subjects compared with young subjects and levels were lower still in the frail elderly group. Plasma cholinesterase also showed a trend towards reduced activity in the frail elderly subjects. As plasma aspirin esterase activity may influence the amount of circulating aspirin, these changes may have implications for the use of aspirin in frail elderly people.