Crown galls developing on leaves and stems of Digitalis lanata plants grown in the greenhouse contained digitalinum verum, glucodigifucoside, deacetyllanatoside C and verodoxin as the main cardenolides. Crown galls formed on leaves of axenic plants accumulated digitalinum verum, strospeside, lanatoside C and glucodigifucoside. These cardenolide profiles differed from those of the tumour-bearing leaves and stems, but resembled that of phloem sap. Crown gall tissue cultivated in vitro did not form cardenolides. However, crown galls in situ and crown gall tissue cultivated in vitro took up cardenolides. Digitalinum verum, a cardenolide characteristic for the phloem sap, was transported to, and accumulated in, the crown galls if administered to tumour-bearing leaves. It may therefore be speculated that the crown galls are sinks for cardenolides transported in phloem sap. The cardenolide-modifying enzymes acetyl-coenzyme A: digitoxin 15'-O-acetyltransferase, lanatoside 16'-O-acetylesterase, UDP-glucose: digitoxin 16'-O-glucosyltransferase and cardenolide 16'-O-glucohydrolase were present in crown gall tissue.