Fludilat (bencyclane-hydrogen-fumarate) increases the O2 consumption and CO2 production of a 10% bovine lens homogenate. An increase of the glucose substrate supply of the homogenate from 25 mM to 37 mM enlarges the above mentioned effects. Investigations on the content of ATP, ADP and AMP show that bencyclane is able to stabilize the physiologic distribution pattern of the three free adenine nucleotides. Changes of the distribution pattern pointing to disturbances of the energy metabolism could in part be normalized by incubation with the addition of bencyclane. This is not only true for lens homogenates but also for whole bovine lenses. Investigations with the enzymes fumarase and malatedehydrogenase indicate that the fumaric acid rest of bencyclane may serve as a substrate for these enzymes in the same way as fumarate. The Km-values found are identical.