Infrared (IR) spectroscopy and thermal analysis have been used to characterize and compare calcium valproate (a compound demonstrating antiepileptic properties) with its different crystalline modifications. We have prepared these modifications by recrystallization from a series of 14 simple solvents. IR spectral differences were observed mainly in the relative intensities of the absorption bands in the regions 3800-3100 cm - 1 , 1700-1500 cm - 1 and 800-400 cm - 1 . This was due to the differences in H-bonded water molecules stipulating the existence of different crystalline states of calcium valproate (pseudopolymorphism). The infrared data were confirmed by thermal analysis.