Chameleon-like scalar field models predict a strong dependence of masses and coupling constants on the ambient matter density. Since matter densities in terrestrial and interstellar environments differ by approximately 15 orders of magnitude, one can test this prediction experimentally through the measurements of relative frequencies in molecular transitions which are most sensitive to changes in dimensionless physical parameters such as, e.g., the electron-to-proton mass ratio. In this talk, I will discuss our recent results obtained with three radio telescopes: 32-m Medicina, 45-m Nobeyama, and 100-m MPR radio telescope at Effelsberg.

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