The authors report on a 66-year-old hemodialysis patient who had diffuse alopecia while on anticoagulation treatment to prevent extracorporeal blood clotting with a low- molecular-weight heparin (LMWH), tinzaparin. The alopecia reversed completely when tinzaparin was substituted by another LMWH, enoxaparin. The biopsy findings, the possible mechanisms of heparin's action in the hair roots, and the restoration of the patient's hairs after the discontinuation of tinzaparin are discussed.