The nonlinear low-field Stark effect in the level n=2 of hydrogen has been investigated. The experiment employed the level crossing technique, measuring the position of the crossings between the Zeeman states: 2P3/2, mj=-3/2 and 2P1/2, mj=1/2; and 2P3/2, mj=-3/2 and 2S1/2, mj=1/2; as the electric field was varied from 0 to 500 kV/m. A beam of atomic hydrogen, produced by thermal dissociation, was subjected to parallel electric and magnetic fields. Lymman –α (Lyα) resonance radiation was generated in an electrodeless microwave discharge lamp. The profile of the Lyα line emitted by the lamp has been investigated experimentally. The level crossings were detected as changes of the Lyα resonance fluorescence intensity observed in a certain direction. The crossing positions were determined from the observed crossing signals of Lorentzian profile by a least squares computer programme. The experimental results for the crossing positions as afuction of the electric field have been compared with theoretical calculations. The theoretical values were obtained by numerical diagonalization of the matrix of the eigenstates |2ljFmF > for perturbation by combined electric and magnetic fields. Radiative corrections were included. Theoretical values and experimental results agreo within the experimental uncertainties of 2%.