Mono- and dihalogenated histamine derivatives incorporating fluorine, chlorine and bromine have been prepared together with the corresponding boc-protected compounds at the aminoethyl group. They have been investigated as activators of the zinc enzyme carbonic anhydrase (CA, EC 4.2.1.1). The cytosolic human (h) isoforms hCA I and II were moderately activated by the boc-protected halogenated histamines and very effectively activated by the deprotected ones. Low nanomolar and subnanomolar hCA I and II activators have been detected for the first time, starting from histamine as lead which has an affinity of 2 μM against isoform I and of 125 μM against hCA II.