Abstract With the purpose of introducing biacetyl bis(2-pyridyl)hydrazone as an analytical reagent, the pyridylhydrazone literature has been reviewed. BBPH acts as a general chromogenic reagent. The fundamental solution chemistry of the complexes formed by BBPH with the metal ions has been studied. BBPH appears to be a promising reagent for the colorimetric estimation of cobalt and palladium. It may be advantageously compared with benzil bis(2-pyridyl) hydrazone which has the same basic chelate structure.