The present study examined whether volunteers with common colds showed impairments in objective and subjective indicators of alertness over the course of the working day. All the volunteers (n=21) were tested when healthy to provide baseline data for simple and choice reaction time tasks, visual search tasks and ratings of mood. These measures were taken before work (08.30 hours), at lunchtime (13.00) and after work (17.30). When participants developed a cold (n,/I>=6) they repeated the procedure. Volunteers (n=15) who remained healthy were recalled as controls and also repeated the procedures. The results showed that those with colds had significantly slower simple and choice reaction times, and felt less alert, more tense and less sociabl...