Polyhydrazides containing pyridine rings in the backbone were synthesized by interfacial or solution polycondensation from 2,5-pyridine dicarboxylic acid and three dihyrazides or hydrazine. Heating conditions suitable for the formation of polyoxadiazoles by dehydration of the polyhydrazides were studied by infrared analysis. The polyoxadiazoles formed were thermally stable but poorly soluble. The polyhydrazides were soluble and could take up cobalt (II) ions. The potential applicability of the polyhydrazides to a reverse osmosis membrane was demonstrated.