Isolated fat cells from male rats were used to study the effects of nicotinic acid and some of its homologues upon lipolysis, adenyl cyclase, phosphodiesterase and cyclic-3’, 5’-AMP production. Only nicotinic acid and 3-pyridylacetic acid inhibited lipolysis, adenyl cyclase and cyclic AMP production consistently although some activity was found with ω(3-pyridyl) acrylic acid. None of the compounds tested altered phosphodiesterase activity. The data suggest that the antilipolytic compounds mediate their effects via the inhibition of cyclic AMP synthesis.