SUMMARYPollen glutamate dehydrogenase is partially present in a masked form. Removal of the masking substances was carried out by several treatments like addition of polyvinylpyrrolidone to the extraction medium, storing of pollen extracts at different pH's and temperatures, fractionation with ammonium sulphate, and incubation with several hydrolytic enzymes. Only the use of polyvinylpyrrolidone and incubation with a few enzymes caused an increase of both amination and deamination activity, whereas the other treatments caused an increase of the amination activity and a decrease of the deamination activity.It is probable that the glutamate dehydrogenase (GDH) and the masking substances are associated through interaction of ionic groups and hydrogen bondings. Some substances may be bound by stronger links. The question whether the masked GDH is present as suchin vivoor whether it is formed during homogenization has been discussed.