Reaction of ethyl or methyl 2-dimethylaminomethylene-3-oxoalkanoates 2 with phenylhydrazine gave the corresponding esters of 5-substituted 1-phenyl-1H-pyrazole-4-carboxylic acids 3 in high yields. Esters 3 were hydrolyzed to the relative carboxylic acids 4, which were converted by heating to 5-substituted 1-phenyl-1H-pyrazoles 5 in excellent yields. Reaction of methyl 5,5-dimethyl-3-dimethylaminomethylene-2,4-dioxohexanoate with phenylhydrazine afforded methyl 1-phenyl-4-pivaloyl-1H-pyrazole-5-carboxylate 8 b, which was converted as above to the corresponding carboxylic acid 10 b and this to 1-phenyl-4-pivaloyl-1H-pyrazole 11 b. Starting from 5-methoxymethyl-1-phenyl-1H-pyrazole, 1-phenyl-1H-pyrazole-5-acetic acid 18 and its alpha-methyl derivative 19 were also synthesized. Compounds 18, 19, 10 b and 11 b showed a strong antiinflammatory activity in rats; the same compounds in general as well as 8 b, showed appreciable analgesic and antipyretic activities in mice and rats, respectively.