The effects of 10 days of total energy deprivation on lymphocyte functions and cell-mediated immunity was evaluated in fourteen healthy, normal-weighted males. Lymphocytes from seven of the subjects were tested in vitro. A significant depression was noted of the DNA synthesis after stimulation with pokeweed mitogen and PPD while there was no effect on the response to concanavalin A. No change was noted in the percentages and total numbers of circulating B and T lymphocytes and monocytes. The delayed skin reactivity following intracutaneous PPD and mumps antigen was not different from non-starving control subjects.