In this case report, the authors, after reviewing the literature data about contrast agents in Magnetic Resonance Imaging (MRI) and correlated problems, investigate the immunological mechanism of an adverse reaction to gadopentetate dimeglumine (Gd-DTPA), in order to demonstrate an IgE-mediated immunological pathogenesis. The case of a patient who underwent MR imaging in our hospital was studied. During, and after, the MR examination with Gd-DTPA the patient showed local warmth/pain to the external genitalia and to the face, tachycardia, nausea, vomiting, diarrhea, uterine cramps, and diffuse cutaneous rash. Skin tests (intradermal) and the passive transfer test according to Prausnitz and Küstner were positive, suggesting the involvement of an I-type allergy (IgE-mediated) mechanism. In this paper, we demonstrate that the adverse reactions to Gd-DTPA can be supported by an immunological mechanism.