We present cytogenetic findings for 12 patients with Alzheimer's Disease (AD) mean age 75.8 +/- 6.01 years and 35 normal age and sex matched controls (mean age 74.8 +/- 4.04 years). The study, undertaken due to reports of increased fragments and chromosome breakage in individuals with AD, was performed blind on coded peripheral blood specimens and the allocation of AD or control was not known to the cytogenetic staff until the end of the study. Both the AD group and the controls have been very carefully selected and both underwent the same clinical assessment and screening procedures which included CT scanning. Chromosomes were analysed after 72 h cultures, using deprived medium TC199 which is known to enhance the appearance of fragile sites. A minimum of 50 cells was examined in each case and any rearrangement found was classified as ctg, csg , ctb , csb and the chromosome in which it occurred was recorded. Analysis of results showed that there was no statistically significant difference between the AD group and the controls for either the total occurrence of breaks, the type of aberration or the chromosome(s) involved. In both groups the commonest break was in 3p .