The structures of trimethylindium (Me3In) adducts with the bidentate tertiary amine N,N,N
′,N
′-tetramethyl-4,4′-methylenebis(aniline)[MBDA] and the macrocyclic amines 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane [N4-aza crown] and 1,4,7,10,13,16-hexamethyl-1,4,7,10,13,16-hexaazacyclooctadecane [N6-aza crown] have been determined by single crystal X-ray diffraction. The adducts have the following stoichiometries, Me3In·2MBDA 1, 2Me3In·MBDA 2, 4Me3In·N4-aza crown 3 and 6Me3In·N6-aza crown 4. Compound 1 contains five-coordinate Me3In in a trigonal bipyramidal configuration and displays the longest In–N bond lengths yet reported (2.720(4), 2.865 Å); 2–4 contain four-coordinate Me3In molecules in a tetrahedral configuration. Compounds 1–4 can be used as intermediate adducts in the adduct purification of Me3In for use in the MOVPE (metal organic vapour phase epitaxy) of InP and related III–V semiconductors.