The effect of N-arachidonoyl dopamine, haloperidol, and their mixture on the rate of tentacle formation was studied during regeneration of the gastral and basal fragments of freshwater hydra. Some concentrations of haloperidol inhibited the tentacle formation, which was more pronounced in the basal fragment. N-arachidonoyl dopamine accelerated the tentacle formation in both fragments, particularly, in the basal one (an inversion of the natural difference in the rate of tentacle formation between the gastral and basal fragments). After the exposure to the mixture of these drugs, the effects of each of them were observed. Mass spectrometry assay has demonstrated endogenous N-arachidonoyl dopamine in the intact hydra homogenate. The possible involvement of this acyl-neurotransmitter in the regulation of the rate of tentacle formation in regenerating hydra is discussed.