In order to elucidate the relationship between the prion protein (PrP) structure and the development of spongiform encephalopathy in zitter rats, we analyzed the nucleotide sequences and restriction fragment length variation (RFLV) of the Prn gene encoding PrP in zitter rats and inbred SD/J rats as a control. Prn genes from two strains had identical nucleotide sequences in their coding sequences. Obvious RFLV on the locus was not detected in zitter rats by a Southern blot hybridization. Consistently, zitter rat brains express the normal cellular PrP (PrPC), but do not accumulate the protease-resistant modified isoform (PrPSC). These results indicate that PrP is not involved in the pathogenesis of spongiform encephalopathy in zitter rats.