Based on our extensive studies of D-glucosidase inhibiting 2,5-dideoxy-2,5-imino-D-mannitol derivatives, we have been trying to create a series of fluorescent derivatives with a view to an 'inhibitory activity ruler' based on competitive displacement reactions of non-fluorescent inhibitors by fluorescent ones and vice versa, which can be performed and followed in microtiter plates or on-chips. Thus, a set of compounds was assembled with Ki values between 2 nM and 1 microM against Agrobacterium sp. beta-glucosidase.