Smoking products, for example cigarettes, cut tobacco, pipe tobacco, cigarillos and the like, give an increased yield of nicotine in the tobacco smoke without impairment of the taste of the smoke, when trans-nicotine N'-oxide, which is free or substantially free of cis-nicotine N'-oxide or contains at most 10% by weight of the cis-isomer, is added thereto in a quantity of up to 5% by weight, relative to the dry weight of the tobacco. The nicotine N-oxide is prepared by oxidizing nicotine with an aqueous H.sub.2 O.sub.2 solution in the presence of a catalytic amount of non-oxidizing acid having a pk value of less than 5 to produce an oxidation mixture containing trans and cis-nicotine N'-oxide.