Summary: The mass suseeptibility of 23 analysed or partially analysed garnets has been measured by means of a calibrated Franz Isodynamic magnetic separator. Straight lines are fitted to the adjusted data for mass susceptibility and molecular composition. The mass susceptibilities of the theoretical end-members in electromagnetic units × 106 are estimated as: almandine, 68±2 e.m.u.; spessartine, 81±3 e.m.u.; and andradite, 49±3 e.m.u. Grossular and pyrope are assumed to have susceptibilities of nil.