During the last 15 years, about 2000 strains of 200 species of 98 genera of fungi have been isolated from around the Chernobyl Atomic Energy Station. Many of these microfungi are capable of growing into and decomposing ‘hot particles’; carbon based radioactive graphite from the reactor and there are suggestions that some fungi actively direct their growth toward sources of radioactivity, possibly attracted to the carbon skeleton of these structures. In our experiments, we eliminated the confounding effects of carbon as a fungal resource, by developing experimental protocols that expose fungal spores and their germinating hyphae to directional sources of ionizing radiation allowing us to measure fungal response to ionizing radiation per se. We show that both beta and gamma radiation promote directional growth of hyphae towards the source of ionizing radiation.