Reaction of methyl 4-methoxy-2-dimethylaminomethylene-3-oxobutanoate with arylhydrazines gave methyl 1-aryl-5-(methoxymethyl)-1H-pyrazole-4-carboxylates 1 in high yields. Esters 1 were hydrolyzed to the relative carboxylic acids, which were converted by heating to 1-aryl-5-(methoxymethyl)-1H-pyrazoles 3 in good yields. Reaction of 3 with hydrobromic acid afforded the intermediate 1-aryl-5-(bromomethyl)-1H-pyrazoles, which were converted with potassium cyanide to 1-aryl-1H-pyrazole-5- acetonitriles, whose hydrolysis gave the required 1-aryl-1H-pyrazole-5-acetic acids. Some acids 5 showed a strong antiinflammatory and analgesic activity in rats and mice, respectively, as well as moderate antipyretic and in vito platelet antiaggregating effects.