This International Standard provides criteria for quality assurance and quality control, evaluation of the performance, and the accreditation of biological dosimetry by cytogenetic service laboratories. This International Standard addresses a) the confidentiality of personal information, for the customer and the service laboratory, b) the laboratory safety requirements, c) the calibration sources and calibration dose ranges useful for establishing the reference dose-effect curves that contribute to the dose estimation from chromosome aberration frequency and the minimum resolvable doses, d) the scoring procedure for unstable chromosome aberrations used for biological dosimetry, e) the criteria for converting a measured aberration frequency into an estimate of absorbed dose, f) the reporting of results, g) the quality assurance and quality control, h) informative annexes containing sample instructions for customer, sample questionnaire, sample of report, fitting of the low dose-response curve by the method of maximum likelihood and calculating the error of dose estimate, odds ratio method for cases of suspected exposure to a low dose, and sample data sheet for recording aberrations.