The relationship between rhythmic reproduction of four stimulus frequencies (44, 80, 126, 200 beats a minute), chosen time, and arousal was studied with 32 subjects of both sexes. The following findings emerged: at the frequency of 44, the group is divided into equal numbers of subjects who either accelerate or slow down; a frequency of 80 induces a general slowing down and a frequency of 200 a general acceleration. Also, the maximum absolute error occurred at a frequency of 200 and the minimum, at the frequency of 80. With regard to chosen time, subjects who tended to accelerate showed a tendency to choose faster rhythms. With regard to level of arousal, the highest frequency was associated with a faster reproduction during relaxed wakefulness and a slower reproduction at the higher and lower activation levels; a state of reduced alertness also produced slowing down at a frequency of 126 and a state of relaxed wakefulness, an acceleration at a frequency of 44.