The in vitro interactions among carbonic anhydrase (CA), acetazolamide (ACTZ), and some short chain acylcarnitines (l- and d-isomers) were studied by means of a recently developed potentiometric method of analysis, based on a pCO2 sensor. The l- and d-isomers of carnitine (C), acetylcarnitine (AC), propionylcarnitine (PC), and isobutyrrylcarnitine (iBC) were found not to affect CA catalytic activity in the absence of other compounds. Upon testing in the presence of ACTZ, the l-isomers of the carnitine congeners were shown to antagonize the chemical inhibition of carbonic anhydrase II from bovine erythrocytes, whereas in this case the d-isomers did not show any effect. The results obtained in these experiments, carried out at 25 and at 37-degrees-C, confirm the high reliability of this new approach and highlight the positive effect of l-carnitine congeners on CA catalytic activity. The potentiometric method should be suitable for monitoring the interaction of other enzymes and CA