Fatty acid composition was identified as a potential biological indicator of the effects of environmental exposure to radiological contaminants. This end point was measured in muscle tissues of Mink frogs (Rana septentrionalis) obtained from a radiologically contaminated pond and from a non-contaminated pond. It was also measured after the frogs obtained from both ponds were exposed to a 4 Gy ⁶⁰Co γ radiation dose delivered in vivo at a dose rate of approximately 8 Gy/min. Statistically significant differences for the increase of a couple of polyunsaturated omega-3 fatty acid residues and the decrease of a polyunsaturated omega-6 fatty acid residue were observed between radiologically contaminated and non-contaminated frogs, indicating a partial remodeling of muscle lipids in response to a chronic low-dose tritium exposure. The effects of an acute high-dose exposure to ⁶⁰Co γ radiation, either for the radiologically contaminated or non-contaminated frogs indicated fast post-irradiation fatty acid changes with an increase of polyunsaturated and decrease of saturated fatty acid contents. Fatty acid composition was found to be a sensitive marker that may be useful to study and monitor biota health in environments that are radiologically contaminated, as well as for understanding the differences between low chronic and high acute stress responses.