In our study we have examined allelic variation of codon 129 among the Polish population as well as Polish and Dutch CJD cases. The open reading frame of the PrP gene was amplified using the polymerase chain reaction (PCR). PCR product was digested with Nsp I and Mae II endonucleases and separated by 2% agarose gel electrophoresis and, finally, sequenced by the Sanger dideoxy-mediated chain-termination method. To obtain population data we have screened 109 unrelated Polish adults. There were 45% of methionine homozygotes, 16% of valine homozygotes and 3% of heterozygotes. Among Polish CJD cases, 75% were methionine homozygous, 12.5% were valine homozygous and 12.5% were heterozygous, whereas among Dutch CJD cases it was 29% of Met/Met and 71% of Met/Val genotypes.