Elevated levels of serum interleukin 2 receptor (IL2R) represent an early measure of T cell activation. The concentration of IL2R was measured in the sera of patients with atopic dermatitis (n = 58) or psoriasis, without psoriatic arthritis, (n = 26), who had moderate to severe disease activity, and in non-atopic healthy controls (n = 37) by an ELISA technique. Serum IL2R levels were found to be significantly elevated in both disease groups compared with the controls. The increase in serum IL2R may be due to T cell activation in the dermis.