There are numerous anecdotal reports relating infection to deterioration in sporting performance. Unexplained failures by top sportsmen are often attributed to recent or current infections. We have carried out a prospective investigation to determine the effect of viral infections on the performance of a group of 68 elite track and field athletes. Athletes were monitored for evidence of viral infection during winter training and their form was assessed subjectively and also semi-objectively by analogue scale questionnaires. Static elevated titres of neutralising antibody to Coxsackie B 1-5 were present in 54% of the athletes and 79% had serological evidence of past viral infection. The raised titres did not relate to poor performance. There was no evidence that loss of form was related to subclinical infection. Elevated antibody levels to Coxsackie B and other common viruses should be interpreted with great caution when assessing athletes complaining of poor performance.