Forty-eight samples of tourmaline from the granitic rocks of south-west England have been analysed by emission spectrography for Fe, Mn, Mg, Ca, Ti, Na, F, Li, Sc, V, Cr, Co, Ni, Cu, Ga, Rb, Sr, Zr, Sn, and Sc. The tourmaline reflects the fractionation trends of the rocks from which it comes in the proportion of Mg, Ca, Ti, and certain trace elements it contains and is considered likely to have been a primary product of the magma. Textural evidence that indicates a later development is interpreted as recrystallization, possibly at low temperature, with little change in chemical composition. Hydrothermal tourmaline has a distinctive chemical composition, being higher in Mg, Ca, Sr, and Sn and lower in Fe, Mn, and F and also tending to have a higher Cr, V, Ni, and Sc content. The chemical composition of the tourmalines is used to show that some quartz-tourmaline rocks are the product of extreme fractionation and are not completely tourmalinized granites. Parti-coloured tourmaline is shown to be the result of hydrothermal growth.