To the Editor: Recent articles in this and other journals have measured lymphocyte subpopulations by means of monoclonal antibodies. However, the authors usually have not stated how blood samples were stored before testing or for how long. We wish to call attention to the effect on the helper/suppressor T-lymphocyte ratio produced by overnight storage of blood samples before testing.Peripheral blood from 13 healthy donors (21 to 35 years old) who took no medications was analyzed. Blood from eight donors was kept at room temperature (22°C) for six hours in an incubator and then stored in a refrigerator at 4°C . . .