Hair growth stages, anagen, catagen and telogen, were diagnosed histologically in skin samples taken at Macquarie Island from 103 southern elephant seals – 11 pups, 56 immatures, 23 adult females and 13 adult males – in order to correlate hair follicle activity with field observations of this species’ unusual type of moult. The duration of the hair growth cycle in fully developed follicles is ∼12 weeks. Hair follicles are active for 2–3 months before, during and after the moult haul-out and are resting at other times of the year. A high proportion of adult females appear to commence hair growth between 4 January and 2 February. While implantation of the blastocyst may be triggered by some astral event, such as daylength, it does not depend on completion of the moult, as suggested by previous authors. The pelage cycle is possibly controlled by an endogenous rhythm established during follicle development and subsequent growth and shedding of the natal coat, but the timing and duration of the moult haul-out may depend on the nutritional status of seals within each particular age–sex class. In adult seals this will be governed by terrestrial activities that involve fasting during the breeding and moulting seasons, whereas immature seals haul out and fast, not only to moult but some also come ashore and rest during winter. There may also be metabolic demands for materials for the complete replacement of the pelage, and much of the stratum corneum.