We investigated in a pilot study on healthy young subjects whether a common cold or a vaccination with influenza virus antigens within 10 days influenced the number and subsets of inflammatory cells in the bronchoalveolar lavage (BAL) fluid. The total number of BAL-cells was about doubled in the common cold group, yet no consistent changes in overall cell distribution was found. Among BAL-lymphocytes the ratio of helper-inducer over suppressor-cytotoxic lymphocytes (THI/TCS) tended to be increased in both groups, due to a lower percentage of TCS-cells, which was significant in the vaccination group only. In the blood, on the contrary, the THI/TCS ratio was significantly decreased in both groups due to a drop in THI-cells; in addition, the proportions of E-Rosette (+) T-cells and of activated (Ia+) T-cells were slightly increased. In conclusion, only minor changes in inflammatory BAL-cells were observed, which, however, may interfere with the effects of other diseases.