The stability of the OR habituation rate as an individual difference trait was investigated in 2 studies. The 1st focused on motor OR's to auditory stimuli at 3 ages within the 1st month of life, and the 2nd examined the HR responses to auditory stimuli at 4 and 8 months. The results indicate that motor OR's did not differ significantly with age and were moderately stable across ages. The stability decreased with age across consecutive days but increased across consecutive weeks. The cross-age correlation for HR responses was moderate. The results were compared with similar findings on other parameters of the OR.