In a double blind study, prazosin, a specific adrenergic alpha₁-receptor antagonist, or placebo were given to 15 females with primary Raynaud's phenomenon. At a low dose (1 mg twice daily) 5 out of 7 of the prazosin-treated patients reported a reduction of attacks induced by cold (p<0.05). this="" was="" not="" confirmed="" by="" a="" cold="" provocation="" test="" which="" showed="" no="" improvement="" at="" finger="" temperatures="" of="" 15="" or="" 10°c.="" the="" highest="" tolerated="" dose="" in="" the="" prazosin-treated="" patients="" varied="" from="" 2–8="" mg="" daily,="" and="" the="" greatest="" number="" of="" side="" effects="" was="" recorded="" in="" this="" group="">p<0.05). none="" of="" the="" patients="" experienced="" complete="" relief="" from="" cold-induced="" attacks.="" it="" was="" concluded="" either="" that="" raynaud's="" phenomenon="" is="" not="" only="" caused="" by="" stimulation="" of="">₁-receptors in digital arteries, or the clinically achievable blockade was insufficient to prevent attacks.