We studied lymphocyte proliferation and subsets in ten atopic dermatitis (AD) patients and ten healthy controls. In addition, monocyte production of interleukin 1 (IL-1) was investigated. Mean numbers of total T cells, T-cells subsets, and B cells did not significantly differ between AD patients and controls even though the patients had slightly decreased amounts of suppressor T lymphocytes. Proliferative responses of AD patients to purified protein derivative of tuberculin (PPD), concanavalin A (ConA), or allogeneic cells did not significantly differ from those of healthy controls at optimal stimulant concentrations. In contrast, at suboptimal concentrations, AD patients showed a diminished response to all of these stimulants. Monocytes from AD patients elaborated clearly less IL-1 than those from healthy controls.