  We report on a new experimental method based on initial-state radiation (ISR)
in e-p scattering, in which the radiative tail of the elastic e-p peak contains
information on the proton charge form factor ($G_E^p$) at extremely small
$Q^2$. The ISR technique was validated in a dedicated experiment using the
spectrometers of the A1-Collaboration at the Mainz Microtron (MAMI). This
provided first measurements of $G_E^p$ for $0.001\leq Q^2\leq 0.004 (GeV/c)^2$.
