The detection of apolipoprotein E genotypes is of importance both for diagnostic and research purposes. We have previously used the polymerase chain reaction to amplify a specific region of the apolipoprotein E gene which, when used in conjunction with allele specific oligonucleotide probes, permits the detection of the six common apolipoprotein genotypes. In our present report we have modified the above procedure by immobilising the amplified DNA using Southern blotting. This enables the technique to be used in routine laboratories with minimal expenditure and little risk of cross-contamination between samples. Furthermore, it is inherently robust and may be rapidly performed.