We have made measurements of the spectrum of resonance fluorescence emitted by sodium atoms in an intense, uniform, monochromatic field. The transition used in the experiment was between the
32S21 (
F=2,
mF=2) ground state and the
32P23 (${F}^{\ensuremath{'}}=3$, ${m}_{F}^{\ensuremath{'}}=3$) excited state. A separate light beam, circularly polarized and resonant with this transition, was used to prepare the sodium atoms in the
F=2,
mF=2 magnetic sublevel. This pumping scheme was used to obtain the spectrum for both on- and off-resonance excitations. The measurements are in good agreement with Mollow's calculation. In addition, we describe conditions under which we observed asymmetric spectra similar to those of earlier experiments.