Dimethylsulfoxide (DMSO) formed a ternary complex when mixed with a Zn-3, 5-diisopropylsalicylate complex of unknown structure. The structure of this new ternary complex was characterized in an initial effort to understand the nature of this compound. Since the original complex is known to have anticonvulsant activity, the new ternary complex was also examined for anticonvulsant activity. The original complex was examined for inhibition of the polymorphonuclear leukocyte (PMNL) respiratory burst in an effort to mechanistically account for zinc complex mediated anticonvulsant activity. Dissolving the structurally unknown complex in DMSO gave crystals of a characterizable complex with an empirical formula C30H46O8S2Zn. Crystallographic data: P 1, Z = 2, a = 8.06(1), b = 12.452(2), c = 17.951(2) A, alpha = 74.42(l), beta = 77.07(1), gamma = 89.50(1) degree. The structure was refined to R = 0.03, RW = 0.04 for 3815 independent reflections with I > 2 sigma(I). This complex is mononuclear, with two 3,5-diisopropylsalicylate ligands and two bonded DMSO ligands, Zn(II)(3,5-DIPS)2(DMSO)2, Zn(II) is coordinate covalently bonded to four O atoms in a strongly distorted tetrahedral arrangement. Each DMSO ligates via its sulfoxide O atom while each 3,5-diisopropylsalicylate ligand is monodentate The non-ligating carbonyl O atom of each 3,5-DIPS is free except for an intramolecular hydrogen bond from the hydroxy group of the same ligand. Both 3,5-DIPS acid and Zn(II)(3,5-DIPS)2(DMSO)2 were examined for anticonvulsant activity in the Maximal Electroshock (MES) and Metrazol (MET) models of seizures and found to prevent both types of seizures. The Zn complex was qualitatively and quantitatively more effective than treatment with the free ligand. The influence of a Zn 3,5-DIPS complex and of the ligand 3,5-DIPS on PMNL oxidative metabolism was also studied to help understand the mechanism of anticonvulsant activity of these compounds. A dose-related and significant decrease in chemiluminescent (CL) response to opsonized Zymosan was observed, and the Zn complex was significantly more effective than the free ligand. It is concluded that mononuclear Zn complexes have anticonvulsant activity in Grand Mal and Petit Mal models of seizure possibly due to inhibition of the synthesis of superoxide or down-regulation of Nitric Oxide Synthase in activated phagocytic cells of the central nervous system.