Ş-aroylacrylic acids (1) react with 3,5-dimethylpyrazole to give a-(disubstituted phenacyl) -3,5-dimethylpyrazol-l-yl acetic acid (2). Reactions of (2) with hydrazine hydrate and phenyl hydrazine afford the corresponding 6-aryl-4-pyrazol--l-yl pyridazinones (3). The behaviour of the pyridazinones with dimethylsulphate, ethyl-bromoacetate, benzoyl chloride, benzenesul- fonyl chloride, bromine-acetic acid, phosphorus oxychloride and phosphorus pentasulfide have been described. The reaction of (2) with aldehyde gives the arylidene derivatives. Dehydration of (2) yields the furanone derivative. The in vitro antibacterial screening reveals mild activity against Gram-positive for compounds (5 b,c) , whilc compounds (2a) and (3e) are inactive.