The inhibition of the two human cytosolic carbonic anhydrase (hCA; EC 18.104.22.168) isozymes I and II with some new pyrazoline derivatives was investigated for the first time. The structures of the newly synthesized pyrazoline derivatives were characterized by Fourier transform-infrared spectroscopy, H-1-/C-13-nuclear magnetic resonance, and mass spectrometry, and elemental analysis. Compounds 1-6 showed K-i values in the range of 16.4-205.9 nM for hCA I and of 6.08-93.21 nM against hCA II. These hydroxyl and amino group-containing compounds generally were competitive inhibitors. The compounds investigated here showed effective hCA I and II inhibitory effects, in the same range as the clinically used acetazolamide, and might be used as leads for generating enzyme inhibitors, possibly targeting other CA isoforms that have not yet been assayed for their interactions with such agents.