Atopic dermatitis (AD) is characterized by alterations in cellular and humoral immunity including elevated serum levels of IgE, IL-2 receptor (IL-2R) and eosinophil cationic protein (ECP). In order to evaluate the relevance of these serum parameters as indicators of disease activity, the concentrations of IgE, IL-2R and ECP were measured in serum samples of patients with an acute exacerbation of AD (n = 19) on admission to hospital and every 6 days up to discharge, and compared with those from normal non-atopic controls (n = 15). The severity of the disease in the AD patients was examined using an established clinical scoring system. On admission, AD patients showed significantly elevated serum levels of IgE, IL-2R and ECP compared with normal controls (P less than or equal to 0.0001). Clinical improvement was associated with a decrease of both the clinical score (P less than or equal to 0.001) and serum ECP levels (P less than or equal to 0.005). No significant changes in serum IgE and serum IL-2R were observed. In addition, there was a significant correlation between serum ECP and the clinical score (R = 0.67, P less than or equal to 0.001). These data indicate that serum ECP may be a helpful tool for monitoring disease activity in AD.