The hyperpolarizabilities gamma of CH4, CF4, and SF6 were measured by the dc Kerr effect at wavelengths from 457.9 to 1092 nm. Vibrational hyperpolarizabilities gamma(nu) were obtained by combining these measurements with electric-field-induced second harmonic generation (ESHG) measurements. The vibrational contribution to the hyperpolarizability ranges from 6% to 35% of the total. At high optical frequency the difference between gamma(nu) for Kerr and gamma(nu) for ESHG is approximately constant, and has values 18, 31, and 51 x 10(-63) C-4 m(4) J(-3) for CH4, CF4, and SF6, respectively. The experimental results are in good quantitative agreement with the results of recent ab initio calculations of the frequency dependence of gamma(nu) for CH4, except for a small but non-negligible discrepancy at high frequency.