Factors that influence growth of the anagen hair follicle have not been defined yet, but there is increasing evidence that cytokines and growth factors are important. Recently we detected an aberrant cytokine expression pattern of the T H 1 type plus IL-1β expression in untreated alopecia areata (AA) totalis and a switch to high IL-10 and TGF-β1 expression levels after successful treatment with the contact allergen diphenylcyclopropenone (DCP). It was now questionable whether cytokines directly arrest the hair growth and whether IL-10 or TGF-β1 are able to block this process. Using whole-organ cultures of microdissected human hair follicles we investigated the effect of a panel of cytokines on hair growth in vitro. IFN-gamma, IL-2 and IL-10 had no effect in this regard, whereas IL-1β completely abrogated hair growth. IL-10, TNF-α, TGF-β1 and PGE 2 where not able to inhibit the IL-1β dependent hair growth arrest. Additionally TGF-α, EGF, TGF-β1 and TNF-α itselves inhibited the hair growth. However, these mediators rather induced a catagen morphology of the hair bulb, whereas IL-1β incubation resulted in the formation of a club-like hair follicle. We conclude that in AA an aberrant expression of, e.g., IL-1β might switch off the hair cycle. However, mediators of the induced contact allergy (IL-10, TGF-β1) are, at leastin vitro , not able to antagonize this process. Therefore we infer that these mediators rather modulate the immune response in AA, possibly by interference with the antigen presentation or expression of adhesion molecules, than directly acting on the hair follicle.