Therefore, we have explored whether thymic peptides alter human hair growth and/or pigmentation in vitro. Instead, we have found that all tested thymic peptides thymulin, Thymosin alpha-1 [TA1], Thymosin-beta4 [TB4]) significantly inhibited hair shaft production of organ-cultured human scalp hair follicles (HF) under serum-free conditions. However, thymulin or TA1-treated hair follicles stayed longer in anagen than vehicle-treated control hair follicles. Nevertheless, TA1-treated hair follicles showed fewer proliferating hair matrix keratinocytes than control hair follicles. Quantitative Masson-Fontana histochemistry revealed further that thymulin-treated hair follicles had significantly more melanin granules than controls. TA1 and TB4 did not influence HF melanogenesis.