Cutaneous fibrinolytic activity was investigated in 13 patients affected with Primary Hypertrophic Osteoarthropathy in the advanced phase. Biopsies were taken from periungueal skin of the ippocratic finger and from the dorsum of the first phalanx: cutaneous fibrinolytic activity was investigated with Todd's autohistographic method as modified by Lotti et al., showing increased activity in periungueal skin (10/13) and normal in the apparently uninvolved skin (9/13). We suggest that the increase in plasminogen activator activity, in the advanced phase of the disease, may be related to the increased growth of the connective tissue that is characteristic of the disease.