We present a pilot study of individuals (liquidators) who were engaged in clean-up operations after the disaster at the nuclear power plant at Chernobyl in Ukraine. In the 10 years since the disaster, adverse health effects among exposed individuals have not been clearly defined. There is widespread fear of damage to the reproductive system, with implications for fertility problems and adverse effects on offspring. Bearing this in mind, methods to evaluate the potential for production of fertile semen have been applied using quantitative ultramorphological (QUM) analysis. QUM analysis examines the organization and integrity of sperm organelles by electron microscopy, using both transmission electron microscopy and scanning electron microscopy. Significant differences were observed between clean-up workers and controls of similar age regarding certain ultramorphological parameters of the sperm head. The results of this pilot study suggest that QUM analysis of human sperm is a feasible approach for evaluating the fertility potential of individuals who were exposed to ionizing radiation from the Chernobyl nuclear power plant accident.