New spiroindoline-substituted sulphonamide compounds were synthesised and their inhibitory effects on the activity of purified human carbonic anhydrase I and II were evaluated. Human carbonic anhydrase isoenzymes (hCA-I and hCA-II) were purified from erythrocyte cells by affinity chromatography. The inhibitory effects of the 14 synthesised sulphonamides (6a-n) on esterase activities of these isoenzymes were studied in vitro. In relation to these activities, the inhibition equilibrium constants (K-i) were determined. The results showed that all the synthesised compounds inhibited the carbonic anhydrase (CA) isoenzyme activity. Among them, 6b was found to be the most active (K-i: 0.042 mu M) for hCA I and 6a (K-i: 0.151 mu M) for hCA II.