ML 23 is a melatonin analogue in the treatment and management of Parkinson's disease. ML-23 is a potential clinical candidate for the treatment of PD, and the present study has been undertaken to determine the efficacy of ML-23 in the 1-methyl-4-phenyl, 1,2,3,6 tetrahydropyridine (MPTP) model in the common marmoset. On all parameters, ML-23 produced a significant remission from MPTP-induced Parkinsonism, and this effect did not abate when ML-23 treatment was withdrawn. Conversely, a recurrence of Parkinsonian signs was not observed when ML-23 treatment was withdrawn and substituted with oral vehicle.