Attachment of the diazeniumdiolate [-N(O)N-O-] functional group to polymers is of increasing interest pharmacologically for their ability to generate up to two molar equivalents of bioactive nitric oxide (NO) spontaneously on exposure to aqueous environments and yet limit physiological effects to sites in close physical proximity. Carbon-bound diazeniumdiolated polymers formed by reaction of NO with the enediamine tautomer of amidines generated on treatment of acrylonitrile-based polymers containing 1,3-dicyano groups are shown to be long lasting NO-releasing materials which may be stored for months at room temperature. NO-releasing derivatives of poly(acrylonitrile) (PAN) powder and fabrics have been prepared and shown to release NO for more than 80 d when exposed to pH 7.4 phosphate buffer at 37 degrees C. PAN/NO powder has been shown to inhibit the formation of neointimal hyperplasia in injured rat carotid arteries. NO-releasing (> 7 d) diazeniumdiolates have also been prepared from poly(styrene-co-acrylonitrile) (SAN resin) and poly(butadiene-co-acrylonitrile) (nitrile rubber). 2,4-Bisdiazeniumdiolated-2,4,6-tricyanoheptane is a carbon-bound diazeniumdiolate that releases NO for more than 200 d in solution in pH 7.4 phosphate buffer at 37 degrees C.