To investigate the short term effects of Doxycycline on MMP-2 and MMP-9. Short term effects of Doxycycline (100 mg B.I.D.) on plasma levels of MMP-2 and MMP-9 were investigated in 20 healthy subjects; the effects of Doxy, Acetylsalicylic acid, Nitrates, and Enalapril on MMP-9 release from were assessed in isolated polymorphonuclear cells. In plasma, MMP-9 activity was reduced (−22%, 95% CI −32/−11; P = 0.002) starting at 12 h after doxy; in vitro, MMP-9 released from stimulated neutrophils was reduced by Doxy (−28%, 95% CI −43/−14; P = 0.001), inhibiting degranulation, and by nitrates (−52%, 95% CI −76/−28 P = 0.005), increasing three times both pro- and active-MMP-9 bound to neutrophils (P = 0.007 and 0.040, respectively). Doxy decreases MMP-9 plasma levels by around 20%, within the first 12 h. The mechanism leading to such reduction seems due to the inhibition of PMN degranulation.