N,N,N'-Triorganylureas and thioureas react either in lithiated or not lithiated form with bromodimethylborane.In the first case, the monomeric N-borylureas and -thioureas 1 - 7 are obtained; in the second case, by-products are 1,3,5,2-triazaborine-4,6-diones (8, 13), 1,3,5,2,6-oxadiazaborin-4-one (10), and 1,3,5,7,2-tetraazaborocine-4,6,8-trione derivatives (9, 12).With N,N'-diorganylureas and -thioureas, resp., the following paths of synthesis were investigated: 1.Lithiation with n-butyllithium (mol ratio 1 : 2) and subsequent reaction with dihalogenoorganylboranes, 2. reaction of the N,N'-bis(trimethylsilyl) derivatives with dihalogenoorganylboranes, 3. reaction with tris(dimethylamino)borane, 4. reaction with halogenodiorganylboranes, 5. reaction with triorganylboranes.In 1. - 4. 1,3,5,2,6-oxa-(thia)diazadiborin-4-one and -thione, resp., (10, 14 - 25, 31 - 36), 1,3,5,2,4-triazadiborin-6-one and -thione derivatives, resp., (26 - 30, 37, 42), and 1,3,5,2-triazaborine-4,6-dione (38) are formed.Path 4. yields also the 1,3,5,2,4-thiadiazadiborin-6-imine 43.By synthesis 5. the N,O-bis(diorganylboryl)isobiuret derivatives, 44 and 45 are accessible.N,N',N''-triorganyl-N,N''-bis(trimethylsilyl)biuret reacts with dihalogenoorganylboranes to give the 1,3,5,2-triazaborine-4,6-diones 11, 39 - 41 and the 1,3,5,2,6-oxadiazadiborin-4-one 40.The compounds were characterized analytically and spectroscopically.