['To investigate the effect of mild manipulations of core and skin temperature on psychomotor vigilance (PVT) in young adults, elderly, and elderly insomniacs.', '432 PVTs were obtained during a 2-day semi-constant routine protocol, while differentially manipulating core and skin temperatures within a comfortable thermoneutral range.', 'Sleep laboratory of the Netherlands Institute for Neuroscience.', 'Groups of 8 sex-matched young adults (27.0 +/- 2.4 years, mean +/- s.e.m.), elderly (65.8 +/- 2.8 years), and insomniacs (59.1 +/-1.9 years).', 'During the 7-minute PVTs, response speed typically declined with increasing time-on-task. Proximal skin warming by only +/- 0.6 degrees C accelerated this decline by 67% (P = 0.05) in young adults and by 50% (P < 0.05) in elderly subjects. In elderly insomniacs, proximal warming slowed down the mean response speed already from the onset of the task (3% level drop, P < 0.001). Response speed tended to decrease with age (P < 0.10), reaching significance only in elderly insomniacs (P < 0.05). Speed decrements occurred mostly towards the end of the time-on-task in young adults; earlier and more gradually in elderly without sleep complaints; and very early and in a pronounced fashion in insomniacs. Interestingly, the worsening by warming followed the time pattern already present within each group.'] Is time-on-task impairment of psychomotor vigilance affected by mild skin warming and changes with aging and insomnia?