In October 1982, a small international symposium was held at the Gesellschaft fUr Strahlen- und Umweltforschung mbH (GSF) in Munich as a satellite meeting of the IX International Conference on Analytical Cytology. The symposium focussed on cytometric approaches to biological dosimetry, and was, to the best of our knowledge, the first meeting on this subject ever held. There was strong encouragement from the 75 attendees and from others to publish a proceedings of the symposium. Hence this book, containing 30 of the 36 presentations, has been assembled. Dosimetry, the accurate and systematic determination of doses, usually refers to grams of substance administered or rads of ionization or some such measure of exposure of a patient, a victim or an experimental system. The term also can be used to describe the quantity of an ultimate, active agent as delivered to the appropriate target material within a biological system. Thus, for mutagens, one can speak of DNA dosimetry, meaning the number of adducts produced in the DNA of target cells such as bone-mar row stem cells or spermatogonia.