Levels of IgE antibodies to Staphylococcus aureus and Staphylococcus epidermidis were determined in eleven patients with typical atopic dermatitis, with no history of furuncles or severe staphylococcal infection. Increased IgE binding to S. aureus but not to S. epidermidis was observed. Fifteen patients with hyperimmunoglobulinemia E-staphylococcal abscess syndrome had increased IgE binding not only to S. aureus but also to S. epidermidis. Other control groups of patients with elevated IgE levels or recurrent staphylococcal infection had normal IgE binding activity to both strains of staphylococci. Interaction of staphylococcal antigens from bacteria on skin with antistaphylococcal IgE antibodies on mast cells could induce mast cell release, evoke itch, and aggravate atopic dermatitis.