Specimens from confirmed cases of Creutzfeldt-Jakob disease (CJD) were examined for evidence of spiroplasma infection. No spiroplasmas or other mycoplasmas were cultivated from brain tissue of 18 cases and no antibodies to several recognised Spiroplasma spp. were detected in sera from 15 patients. These negative cultural and serological results provide no support for published suggestions that CJD brain contains structures morphologically resembling spiroplasmas.