An approach to combine the advantages of random and of focused combinatorial libraries in pharmaceutical research is described with the example of a solid phase synthesis of 2, 5- disubstituted thiadiazole ethers. Key steps of synthesis are the introduction of the heterocycle by selective, sequential nucleophilic double substitution of 2, 5-bis (methylsulfonyl)-1, 3, 4-thiadiazole and the oxidation of the benzylsulfanyl-1, 3, 4- ...