NADH dehydrogenase (EC 1.6.99.3) mutations at nucleotide 5460 of mitochondrial DNA (codon 331 of the ND2 subunit gene) have been associated with Alzheimer's disease (BBRC 182, 238-246, 1992; BBRC 189, 1202-1206, 1992). We have sequenced codons 304-347 of this gene in 15 neuropathologically confirmed cases of Alzheimer's disease. In addition, restriction enzyme analysis was performed on the same cases and on 28 control brains. No mutations were detected in the Alzheimer brains but heteroplasmy for a G-->A transition at nucleotide 5460 of mtDNA was found in the frontal cortex of a single control. Thus, our findings do not confirm reports of a significant association between mutations at nucleotide 5460 of mitochondrial DNA and Alzheimer's disease.