Anticoccidial 1-substituted 4(1H)-pyridinone hydrazones

4-Chlorobenzaldehyde 1-(4-chlorophenyl)-4(1H)-pyridinylidene hydrazone fluorusulfonate (4) was found to have excellent anticoccidial activity in chickens. The synthesis and biological evaluation of related analogues are presented. Presumably 4 shares a common mechanism of action with robenidine (25) since it was not active on a robenidine tolerant strain of E. tenella. Structural comparisons of the two molecules are presented.