AbstractIn intact female rats and in one receiving hormonal treatments which alter spontaneous follicular cycles, hairs were plucked before, during or after the spontaneous growth of G2 hairs. Several successive hair eruptions on the epilated and the contra‐lateral intact flank were then observed.Epilation always advanced the next eruption, except that if performed during the last few days before spontaneous eruption was expected, it had no effect.Eruption after a fixed interval characteristic of the region epilated followed the plucking of club hairs from resting follicles. After growing hairs were plucked, the interval to eruption was longer, and varied with the stage of anagen reached at epilation. Nevertheless the advance of eruption was even greater than after the epilation of resting follicles. The interval from epilation to eruption was increased by estradiol or propylthiouracil, which prolong both spontaneous and induced follicular cycles, and reduced by spaying or thyroxine, which shorten them.Under all treatments, epilation also advanced subsequent eruptions, the second usually even more than the first. Comparison of cycle lengths of epilated and normal follicles, and correlation with observations on pulse‐labelled hairs, showed that while the first post‐epilation anagen was unaltered, the resting phase which followed it was shortened. Subsequent cycles tended to be prolonged.Some evidence was found for a slow‐acting systemic control tending to resynchronize the cycles of epilated follicles with those of symmetrically‐placed nonapilated ones, although complete synchrony was not achieved within three or four cycles of a single epilation.