Improved polymer blends comprise (a) a linear alternating polymer of carbon monoxide and at least one ethylenically unsaturated hydrocarbon, (b) a polymeric polyamide, (c) a maleated, partially hydrogenated elastomeric block copolymer, and optionally (d) an acidic polymer of an .alpha.-olefin and an .alpha.,.beta.-ethylenically unsaturated carboxylic acid wherein, optionally, a portion of the carboxylic acid groups have been neutralized with non-alkali metal. The blends demonstrate a good balance of strength and toughness.