The main results of the study are that in the early stages of PPID (a), clinical signs can be subtle or absent; (b) basal ACTH concentrations are variable between months and frequently equivocal; (c) increases in ACTH concentrations especially in the autumn can be markedly increased prior to the development of hypertrichosis; (d) TRH-stimulation testing in late summer or autumn may be useful for identification of most transitional cases. Here, TRH is linked to hypertrichosis.