ABSTRACTMonthly regrowth of clipped hair was measured in greyhounds over a two‐year period; plasma progesterone and testosterone were measured at the time of clipping.Entire males and females showed virtually no growth in late winter and late summer while maximal growth occurred in mid‐summer. Oestrus, and its associated hormones, appeared to suppress hair growth in entire females while spayed females showed good growth throughout most of the year.Low environmental temperature was considered to depress growth in late winter.