Cefadroxil, a cephalosporin, had been prescribed to children with superinfected atopic dermatitis, and was shown to improve both the infection, the clinical status and induced a dramatic lowering of the serum total IgE levels. Further studies have confirmed the IgE immunomodulating properties of cefadroxil. We report the case of a 3 year old asthmatic child who was hospitalized for superimposed pneumonia and was included in a study evaluating cefadroxil. The child was also suffering of juvenile rheumatoid arthritis. After treatment with cefadroxil and oral salbutamol, the child fully recovered. The initially elevated serum IgE (day 1:556 IU/ml) dropped to normal values (day 21: 52 IU/ml), while the production of IgE in vitro by peripheral blood B cells was normalized. We suggest that one mechanism of action of cefadroxil is the stimulation of production of gamma interferon in patients with atopic disorders; this mechanism interferes with the IL-4 primary signal, as well as with other second signals recognized for the synthesis of IgE. Gamma interferon may also prove beneficial for the control of juvenile rheumatoid arthritis.