Body temperature is a basic indicator of health. Intracellular temperature is also a basic indicator of cellular health; cancer cells are more metabolically active, and thus can have a slightly higher temperature than healthy cells. However, until now the available tools for testing such hypotheses haven't been up to the task. In a study recently published in Nano Letters, researchers from Osaka University and collaborating partners have experimentally measured temperature gradients within human cells and at unprecedented precision. This study will open up new directions in drug discovery and medical research.