Polymorph Form III of N-methyl-N-(3-{3-[2-thienylcarbonyl]-pyrazol-[1,5-alpha]-pyrimidin-7-yl}phenyl)acetamide, and use thereof as a sedative-hypnotic, anxiolytic, anticonvulsant, and/or skeletal muscle relaxant agent. Related compositions and methods are also disclosed, particularly with regard to treatment of insomnia.