Carbonic anhydrase (CA) is an enzyme which plays role/roles in various homeostatic mechanisms, such as the acid-base balance and electrolyte secretion in various tissues. This study aimed to determine and to compare possible alterations in activity of this enzyme caused by use of bronchodilator drugs and respiratory infection antibiotics. CA I and II were purified from human erythrocytes by a simple one step procedure using Sepharose 4B-L-tyrosine-sulfonamide affinity column. The iso-enzymes were purified 259.16-fold with a yield of 31.74%. CAI and II isozymes were treated with several drugs, then the inhibition or activation of the enzymes were determined. The results of this study show that itrapropium bromide is the most effective inhibitor for human erythrocytes carbonic anhydrase compared with the other bronchodilator drugs.