Fluorescence in-situ hybridization using whole chromosome probes (FISH-WCP) has become the methodology of choice of most cytogenetic laboratories. However, good hybridization results are often associated with sample quality, storage conditions, and the age of metaphase preparations. Particularly, aging metaphase preparations over a prolonged period of time has been considered a critical and limiting factor in FISH success. This study reports on the successful use of the FISH-WCP procedure to hybridize chromosome preparations that were aged for approximately 12 years. Biological samples consisted of 4 individuals accidentally exposed to cesium-137 in Goiânia (Brazil) in 1987 and 1 control individual. Metaphase spreads were obtained from conventionally PHA-stimulated T lymphocytes from peripheral blood. Aged slides underwent treatment with Carnoy's fixative for 16 h, followed by exposing the slides to water-bath vapour at 60 degrees C for 4 h. During analysis, chromosome type aberrations, including translocations, acentric fragments, and dicentrics were observed. The results suggested that it is possible to validate the use of FISH-WCP as a method of choice to study aged chromosome preparations, even if the slides were stored in undesirable conditions of temperature and humidity. Under these circumstances, the procedure could possibly be used as a potent tool in retrospective dosimetry.