The number of oil ducts in freehand sections of roots of eight carrot (Daucus carotaL.) genetic lines was compared to the levels of major volatile terpenoids. There was a high correlation (0.79) between number of ducts per unit area and total terpenoid amount. Individual compounds exhibited varying degrees of correlation, probably due to genetic difference between lines. Oil ducts often exhibited distinct patterns of concentric rings or radial lines, but this feature was not closely related to duct number. Oil ducts are present only in the phloem, and can form a highly interconnected network.