In this study designed to compare the relative pacifying properties of horizontal and vertical rocking, 13 infants (mean age--58 days) were each tested on two subsequent days. The rocking device was a cradle that could be manipulated to produce side-to-side rocking similar to a commercial cradle or up-and-down rocking. In its up-and-down mode, the cradle was moved through a 4-inch vertical excursion. Each subject received one mode of rocking in one daily session and the other mode on the following day. The subject's activity was independently rated on a 6-point scale every 30 seconds by two observers, and by an Electro-Craft Movement Transducer placed under the mattress of the cradle. Each day the infant received two 5-minute periods of rocking preceded and followed by a 5-minute observation period. Scores showed that activity during rocking decreased; but with termination of rocking, activity returned to the baseline level following the first rocking period. Activity after the second rocking period did not rise to the initial level. The up-and-down mode was more effective as a soother than the side-to-side mode. Transducer scores were in agreement with observer scores. (Author/AJ)