The introduction of a carbamate warhead (most often the ethylmethyl carbamate of rivastigmine as in 1c or phenyl carbamate) on a variety of scaffolds easily produces BChEIs. However, a word of caution: especially in the field of cholinesterases, the literature is filled with examples of "IC 50 -value-only" ChEIs that lack full and correct confirmation of their covalent modes of action. Taking advantage of the BChE broad substrate recognition and promiscuous binding due to the large, hydrophobic active site, such compounds can easily bind reversibly with micromolar affinities. An example from our research group nicely shows that the presence of the carbamate moiety in a BChE-active compound does not simply guarantee a covalent mechanism of action. As with all of the other covalent inhibitors, the carbamate inhibitors must also be carefully optimised, in terms of both electrophilicity and reactivity of the warhead itself, and with regards to the correct orientation and steric requirements that allow for the covalent modification to proceed. Although IC 50 values do not allow for a full characterisation of covalent inhibitors, within a series of compounds. a comparison of the ligand IC 50 values at a fixed timepoint can be both valid and rapid in a fast-moving drug discovery programme compared to the determination of the exact k inact /K I values. In our hands, the following "triage" of testing potential covalent inhibitors is used: the IC 50 values are determined at different timepoints to ascertain the timedependency profile (decreasing IC 50 values with longer preincubation times are indicative of a special mechanism of binding ), the hits with pronounced or inconclusive time-dependent profiles are then confirmed by kinetic analysis (via k obs from initial velocity measurements or full progress curve analysis ), with the final unequivocal proof provided by crystallisation or LC-MS, or both.