[Show abstract][Hide abstract] ABSTRACT: The body temperature and locomotor activity rhythms of seven 1-Methyl, 4-phenyl, 1,2,3,6-tetrahydropyridine (MPTP)-treated cynomolgous monkeys were registered over a week on two separate occasions over an interval of 2 months. Motor disability was absent in two animals and present in five: it was mild in one, moderate in two and severe in two. Both temperature and motor activity were recorded every minute using a radio telemetry system. Analysis of circadian rhythms revealed less robustness of the 24-hour circadian components of body temperature and locomotor activity with increasing motor impairment, and a fragmentation of the body temperature rhythm into 8 hour-period components. Both total activity and daytime activity correlated inversely with the degree of motor impairment. On the contrary, the monkeys did not show differences in night time activity. The proportions of variance accounted for by the body temperature and locomotor activity of 24 h + 12 h + 8 h components were correlated. Also, the average levels at which the circadian rhythm varies between body temperature and locomotor activity were correlated. The results were almost identical in the two 1-week recording sessions. The present study confirms individual differences in the vulnerability to MPTP of the nigrostriatal system of monkeys, suggesting that if a cumulative dose does not provoke stable motor alterations, this cumulative dose will not produce circadian body temperature and locomotor activity rhythm alterations either. Similarly, if a dose is able to produce motor impairment, this dose will also be able to produce circadian rhythm alterations.