A new strain, Claviceps purpurea 88-EP-47, with high invertase activity was selected. Free and Caalginate immobilized cultures of this strain were used for fructosylation of ergot alkaloids. By bioconversion from their aglycones, elymoclavine-O-/~-o-fructofuranosyl(2~l)-O-fl-D-fructofuranoside, and elymoclavine-O-fl-D-fructoside, the respective fructosides of chanoclavine, lysergol and dihydro-lysergol monofructosides were obtained. These substances are formed by fl-Dfructofuranosidase present in Claviceps cells. The bioconversion activity of the enzyme system (fructose transfer) is strongly dependent on pH, substrate (sucrose) concentration and the developmental profile of invertase activity. The pH optimum for elymoclavine fructosylation is 6.5, for chanoclavine 5.7, and the optimal sucrose concentration is 75 g/1. Fifteen-day-old production cultures had the best glycosylation activities. Fructosylation of alkaloids can be stimulated in production cultures of C. purpurea or C. fusiformis forming elymoclavine or chanoclavine by a pH shift to 6.5 at the end of the production phase. Glycosylating Claviceps strains producing elymoclavine eliminate the free alkaloid into glycosides. The feedback inhibition of alkaloid synthesis by elymoclavine is then strongly reduced, helping to further improve elymoclavine yields. Elymoclavine can be liberated simply by invertase activity of baker's yeast.