Paul Dirac first put forward the idea of the magnetic monopole - a particle that carries an isolated north or south magnetic pole - in 1931, but all experimental searches for these elusive particles have proved fruitless. However, a group of physicists from Japan, China and Switzerland are now claiming that they have found indirect evidence for monopoles. The team observed an anomalous Hall effect in a ferromagnetic crystal that they say can only be explained by the existence of magnetic monopoles (Z Fang et al. 2003 Science 302 92).