To study the underlying mechanism of gonadal growth during the attainment of puberty and to test a coincidence model, 7 experimental groups of 2-week-old male mice, Mus musculus, were administered the serotonin precursor, 5-hydroxytryptophan, followed by the dopamine precursor, L-dihydroxyphenylalanine at hourly intervals of 6, 7, 8, 9, 10, 11 and 12 h (5 mg/100 g body weight per day for 13 days). At 11 days post-treatment, a suppression of gonadal activity was seen in the 7-h mice and a maximum suppression in the 8-h mice, along with a significantly increased degree of gonadal development in the 12-h mice, as compared with the controls. In addition to its known regulation of seasonal gonadal cycles, the relative position of two circadian neural oscillations may also affect the rate of gonadal development during the attainment of puberty in mice. Moreover, the present study provides an experimental paradigm to test the coincidence model of circadian oscillations.