Sib-pair linkage analyses were used to search for linkage to a set of chromosome 19 and 21 marker loci in two sets of families with Alzheimer's disease. The advantage of this technique is that no assumption is made about the mode of inheritance of the disease. Some mild suggestions of linkage were found in early-onset families for a chromosome 21 marker and in a set of late-onset families for a chromosome 19 marker.