Phospholipase D from cabbage or Streptomyces chromofuscus catalyses the transesterification of alkylphosphate esters, which are potent antitumor agents. The exchange of choline in octadecylphosphosphocholine by N-(2-hydroxyethyl)-N-methylpiperidine with phospholipase D from cabbage is kinetically controlled and amounts to maximum 60% in buffer, 43% in buffer/n-hexane, and 82% in buffer/n-hexane/1-octanol.