Vibronic features are observed in the excitation spectrum of Pr3+ in several host lattices. Vibronic transition probabilities, AVIB, for the 3H4 to 3P0 excitation transition on Pr3+ are reported. AVIB varies by two orders of magnitude from LaF3 to Y2O2S. These observations are discussed in terms of existing theories of the intensity of vibronic transitions in the intraconfigurational 4fn spectra. The observed variation can be qualitatively accounted for by the differences in covalency, polarizability and opposite-parity configuration admixing.