The aim of this study was to screen leukocyte cell surface markers to identify possible predictors for infection related to physical training. Ten healthy soldiers (mean age, 19.1; mean body mass, 77.4 kg; mean VO2 peak, 4.54 L min(-1)/58.6 mL min(-1) kg(-1)) were included. Blood samples were collected and number of infections recorded before and after a 6-day training course. White blood cell distributions and expression of surface receptors changed during training. Before training, expression of CD3 on CD8+ lymphocytes and percent CD8+CD3 lymphocytes was lower, whereas CD4/CD8 ratio was higher among subjects who failed compared to those who completed the training. A subclinical infection before the start of the military training may alter the CD4/CD8 ratio. Prediction of future infections may be possible from pre-exercise immunological status, findings useful in military settings and exercise, where sudden infections may result in severe consequences.