The specific aim is to investigate the Pharmacological properties of silylated derivatives of known active organic molecules and to identify biologically active organosilicon compounds that do not have known carbon analogy. Active organosilicon compounds without carbon analogy appears to offer the greatest potential for future discovery of new medicinal compounds. The branched-chain organosilicon compounds with three or four silyl groups directly bonded to a carbon or silicon atom have no analogy in organic chemistry, therefore, considerable efforts will be devoted to studies of their activity. Also, synthesis and pharmacology of silylated derivatives of known medicinal . compounds will be investigated to establish correlations between the effect of the space-filling, lipophilic silyl groups and biological properties.