The present invention relates to an improved process for determining γ-secretase activity and for detecting γ-secretase, a subunit protein of γ-secretase, or a γ-secretase-like proteinase. In particular, the present invention relates to processes for the identification of a γ-secretase or of a cDNA which codes for a γ-secretase, a subunit protein of γ-secretase, or a γ-secretase-like proteinase. Another embodiment of the present invention relates to processes for the identification of substances which can inhibit the activity of γ-secretase, or a γ-secretase-like proteinase.