Peripheral lymphocytes of 6 patients with late-infantile amaurotic idiocy were examined with the electron microscope for the occurrence of curvilinear bodies and fingerprint structures. In 3 of the patients predominantly curvilinear bodies were found; in 1 case they contained some fingerprint profiles. In the remaining 3 patients curvilinear bodies were relatively scarce, whereas fingerprint structures prevailed. Moreover, pleomorphic bodies with rectilinear profiles and parallel tubular inclusion bodies were present. No lymphocytes with vacuoles were observed in any of the patients. The sural nerve biopsies of all patients revealed curvilinear bodies. This tissue consequently may be considered to give more reliable information in comparison with the lymphocyte. The likelihood of transition of one type inclusion body into another, the specificity of the curvilinear body and, to our mind, the rigid classification of the amaurotic idiocy into a curvilinear and a fingerprint type, are discussed.