Abstract In obtaining fission-track ages for meteorites, the effects of cosmic-ray primaries and induced fission must be taken into account. The presence of 244Pu tracks allows the cooling rates of meteorite parent bodies to be determined with good time-resolution. Chondrites and IA irons cooled at rates of a few degrees K per Myr and probably originated in bodies of ∼ 100 km in radius. The mesosiderates cooled rather more slowly. No fission-track evidence for the existence of extinct superheavy elements in meteorites has yet been obtained.