Several alkylmagnesium alkoxides have been prepared by alcoholysis of the dialkyls in diethyl ether, and can be obtained free from ether. In benzene, EtMgOPrn, PriMgOMe, and PriMgOEt are oligomers (degrees of association ca. 8), but those alkoxides we have studied in which there is chain-branching α to oxygen are tetramers, (EtMgOPri)4, (EtMgOBut)4, and (PriMgOPri)4. The 3-ethyl-pentan-3-ol derivative, from Et2Mg + Et2COor Et2Mg + Et3COH, crystallises as an ether complex (EtMgOCEt3,Et2O) which loses ether very readily: the tetrahydrofuran adduct is dimeric in benzene (EtMgOCEt3,THF)2. Some alkylmagnesium alkoxides are tetramers in diethyl ether, (EtMgOEt)4, (MeMgOBut)4, and (EtMgOBut)4, but two are dimers, (EtMgOCMeEt2)2 and (EtMgOCEt3)2. Methylmagnesium t-butoxide disproportionates in dilute solution in benzene. Both dimethyl-magnesium and ethylmagnesium ethoxide crystallise from diethyl ether at room temperature without solvent of crystallisation. The diethyl ether complex of t-butoxymagnesium bromide crystallises from the solution obtained when acetone is added to methylmagnesium bromide in ether. It is a dimer, (ButOMgBr,EtO)2, both in benzene and in ether and in the crystalline state. Several analogous products have been obtained by other similar reactions, and all those whose molecular weights were measured were also dimeric (solvent given) examples are (ButOMgBr,THF)2(benzene), (Et3COMgBr,THF)2(benzene), (Et2MeCOMgBr,Et2O)2(ether), (Et2MeCOMgl,Et2O)2(ether), (Me2PrnCOMgl,Et2O)2(ether), t-Butoxymagnesium bromide-diethyl ether complex has also been prepared from magnesium bromide and both Mg(OBut)2 and MeMgOBut. The 1H n.m.r. spectra of several of the compounds described are anomalous in unexplained ways.