Results from our research on the effects of colds and influenza on performance have led to the following conclusions. First, these illnesses have significant effects on performance efficiency, although the nature of the impairment depends on the type of virus and the task being performed. For instance, influenza slows reactions to stimuli appearing at irregular intervals, or in unknown locations, whereas colds impair hand-eye co-ordination. Performance impairments have also been found with sub-clinicial infections, during the incubation period of the illness, and after the symptoms have gone. These results have important implications for occupational safety and efficiency.