Almost no work exploring the effects of stimulus onset and offset is to be found, especially if one looks at the problem in a developmental manner. In order to investigate this problem, a total of 62 infants within the first year of life were seen: 22, 20, and 20 subjects at 12, 14, and 52 weeks respectively. Each infant received seven trials, 30 seconds in duration, with a 30-second intertrial interval. The first six trials consisted of the same auditory signal--a C chord at 65 db--while the seventh trial was either a C tone or a C chord with the base notes muted (dull), both at 65 db. Heart rate was continuously monitored along with other measures not reported in this paper. Amount of deceleration was used as the primary response. The data indicate several important results: (1) a consistent and rather large degree of deceleration; this for both onset and offset. (2) For 3- and 6-month-olds the terminal OR is less than the onset OR, while the 12-month olds show greater terminal than onset OR. (3) Habituation of the onset OR follows a developmental pattern, with 3-month olds showing the least habituation and 12-month-olds showing the most. (4) Habituation of terminal OR also shows a developmental trend, with the 3- and 6-month-olds showing habituation while 12-month-olds showed little habituation. The recovery data results for the seventh trial indicate that some changes are more effective than others.