Microwave radiometry may be used as a non-invasive technique for subcutaneous thermal sensing. This technique was capable of demonstrating extravasation of small volumes of fluids, including the antineoplastic agent adriamycin, when these fluids were administered at room temperature in dogs. The rate of temperature drop upon extravasation was proportional to the flow rate. It is feasible that microwave radiometry may be useful as an alarm system to reduce serious complications which often accompany the extravasation of antineoplastic drugs.