1.N-Methylpyrazoles, which have both electron-donor and electron-acceptor substituents in the 3 or (and) 5 positions, undergo oxidative iodination by I2-HIO3mixture. Here the halogen atom can be inserted successively in the 4 position and then in either the free 5 or 3 position.2.N-Methylpyrazole-4-carboxylic acids and 4-aldehydes under the conditions of this reaction undergo substitutive iodination and form either the 4-iodo or polyiodo derivatives.3.The presence of moderately strong electron-acceptor substituents (I, COOCH3) in the 4 position of the pyrazole ring does not exclude the possibility of oxidative iodination in its other positions. Strong acceptor groups (NO2) in the 4 position prevent the reaction.