An enzymatic method is described for the pH-stat determination of a series of alkaloids, vitamins, sulfonamides and anions based on the inhibitory effect on the cholinesterase-catalyzed hydrolysis of butyrylcholine iodide (BuCh). All analyses were done at 25.0°C and pH 8.00 Creadable reproducibility of ± 0.02 pH unit)- Sensitivity ranges from 13 ng (physostigmine) to 0.86 g (niacinamide). The precision is < 2.0% with the exception of physostigmine which is ≤ 5.2%. The average recovery and analysis times were (98.1–104.1)% and 10 min., respectively. Complete Inhibition curves are presented and the relative inhibitory “potency” of the compounds examined is inferred.