The increasing knowledge about the carcinogenic properties of asbestos have given rise to an extensive research on possible adverse health effects of alternative materials. Especially man-made mineral fibers (MMMF), i.e. glass fibers, but also glass-, stone- and slag wools turned out to be of unique interest, because they have already been used for several decades for isolation purposes. It is generally accepted that the carcinogenic potential of any fiber is related to its dimension and its biopersistence. Based on series of experiments, it could be demonstrated that only fibers longer than 5 microns, thinner than 3 microns and with a length/diameter ratio of more than 3 are able to reach the periphery of the lung. Excepting the refractory (ceramic) fibers, studies showed that inhalation did not provoke tumors in rodents, whereas the intratracheal, intrapleural and intraperitoneal instillation induced a carcinogenic effect for most kinds of MMMF. Compared to asbestos, MMMF clears out much faster from the lung tissue. Finally, there is no consistent epidemiological evidence for an increased standardized mortality ratio due to malignant tumors of the airways and malignant mesotheliomas in individuals formerly exposed to MMMF. Out of the rather theoretical tumor risk, there is a far more common and itchy skin problem to mention, namely glass-fiber dermatitis, which appears when one is handling without protection thicker and therefore more stinging fibers. In the light of these facts and based on the actual exposure situation, there is no clearcut cancer risk, when one is handling glass fibers and wool; however, the potential risk of exposure to refractory ceramic fibers has to be evaluated with more caution.