Electron spin resonance absorption spectra of cesium and rubidium solutions in ethylamine have been observed at temperatures between -29° and +23°C. These spectra are characterized by a sharp single-line resonance near the center of a hyperfine pattern. The lines of a hyperfine pattern vary in amplitude and breadth. The larger amplitude, narrower lines lie near the center of the spectrum. The hyperfine patterns are attributed to 85Rb and 1330Cs nuclei interacting with an unpaired electron. The spin density at the 85Rb nucleus varies from 1.05±0.1×10 24 cm3 at -25°C to 1.90±0.05×1024 cm 3 at 23°C and at the 133Cs nucleus from 2.29±0.03×1024 cm3 at -29°C to 2.80±0.03×1024 cm3 at -10°C. The variations in Une breadths are interpreted in terms of the structure of the metal monomer. The difference in g values between the singleline resonance and the hyperfine pattern is attributed to spin-orbit coupling in the monomer and structural implications are discussed. The single-line resonance is assigned to the solvent anion, i.e., the solvated electron.