The electron affinities have been measured for trimethylgermanium and trimethyltin radicals as 31.9 +/- 0.7 and 39.2 +/- 1.5 kcal/mol, respectively, using electron photodetachment spectroscopy. The acidities (Delta H degrees(acid)) for the corresponding hydrides (Me(3)GeH and Me(3)SnH) have been bracketed as 361.5 +/- 2.8 and 349 +/- 2 kcal/mol. From the electron affinities and the acidities, the D degrees(Me(3)MH) are derived as 79.8 +/- 3.5 and 75 +/- 3.5 kcal/mol, respectively. These physical properties are compared with the properties of the group IVA through group VIIA binary hydrides and methyl-substituted compounds. The electron affinities of the group IVA compounds do not conform to the regular pattern; some of the reasons for this are discussed.