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Wave functions, energies, and binding energies for the lowest singlet states of H- and He in uniform magnetic fields B<109 G are calculated using an adiabatic approximation in hyperspherical coordinates. In computing the angular part of the wave functions, a coupled expansion in one-electron oblate spheroidal angle functions is used. In addition to contracting the two-electron wave function radially, the magnetic field is found to distort the angular part of the wave function mainly by reducing the ss1S character of the state and replacing it with an sd 1D character. Results for energies and binding energies are comparable with those obtained in variational calculations. In order to compute the binding energies of H- and He we have also calculated the binding energies of the ground states of H and He+ in uniform magnetic fields B<109 G using the adiabatic oblate-spheroidal-coordinate method of Starace and Webster.