The ergot alkaloids elymoclavine, ergometrine and chanoclavine were alpha-mannosylated with alpha-mannosidase as catalyst. The kinetic reaction with p-nitrophenyl alpha-mannoside as glycosyl donor gave ca 28 % yield of chanoclavine alpha-mannoside, whereas the equilibrium reaction with mannose as the glycosyl donor gave ca 11 % yield. However, in the case of elymoclavine and ergometrine, higher yields of alpha-mannosides were obtained with the equilibrium approach (18 and 13 %).