The purpose of this document is to provide criteria for quality assurance (QA), quality control (QC) and evaluation of the performance of biological dosimetry by cytogenetic service laboratories. This document addresses: a) the responsibilities of both the customer and the laboratory; b) the confidentiality of personal information, for the customer and the laboratory; c) the laboratory safety requirements; d) sample processing; culturing, staining and scoring, including the criteria for scoring for translocation analysis by FISH; e) the calibration sources and calibration dose ranges useful for establishing the reference dose response curves that contribute to the dose estimation from chromosome aberration frequency and the detection limit; f) the scoring procedure for translocations stained by FISH used for evaluation of exposure; g) the criteria for converting a measured aberration frequency into an estimate of absorbed dose (also appears as dose ); h) the reporting of results; i) the QA and QC; j) Annexes A to F containing sample instructions for the customer, sample questionnaire, sample datasheet for recording aberrations, sample of report and fitting of the low dose-response curve by the method of maximum likelihood and calculating the uncertainty of dose estimate.