Infrared absorptions due to the BeH₂Be bridge in Na₂(CD₃)₄H₂Be₂ are at 1333 and 1164 cm.^–1, confirming earlier assignments for this structural unit. The spectra of the trimethylamine and the tetramethylethylenediamine complexes of (CH₃)₂Be and (CD₃)₂Be are compared, as are the trimers [CH₃BeN(CH₃)₂]₃, [CD₃BeN(CH₃)₂]₃, and [CH₃BeN(CD₃)₂]₃. Absorptions due to Be–CH₃ symmetric deformation occur in the range 1186–1206 cm.^–1, ν_H/ν_D being close to 1·22. Beryllium–methyl stretching vibrations are not clearly identified, but appear to be in the range 700–900 cm.^–1. The chemical shifts of the methylberyllium protons in complexes of dimethylberyllium with trimethylamine, diethyl ether, and tetramethylethylenediamine are compared with the values of the chemical shifts of methyl groups attached to other electropositive elements. The proton magnetic resonance spectrum of the trimer [(CH₃)BeN(CH₃)₂]₃ is consistent with a six-membered ring structure undergoing rapid interconversion in the temperature range –90 to +25°.