The carbohydrate polymers known as β-1,3-d-glucans exert potent effects on the immune system — stimulating antitumour and antimicrobial activity, for example — by binding to receptors on macrophages and other white blood cells and activating them. Although β-glucans are known to bind to receptors, such as complement receptor 3 (ref. ), there is evidence that another β-glucan receptor is present on macrophages. Here we identify this unknown receptor as dectin-1 (ref. ), a finding that provides new insights into the innate immune recognition of β-glucans.