We have synthesized the solid solutions of Fe1−xCoxGe compounds with x running from 0.0 to 0.9. Small-angle neutron scattering and magnetization measurements have shown that these compounds are ordered into the spin helix structure below the critical temperature Tc. The helix is transformed into the ferromagnet by application of the magnetic field above the critical value Hc2. It is shown that Tc decreases smoothly with concentration x from 280 K for FeGe to 0 for CoGe. The values of the helix wave vector ks and the critical field Hc2 depend strongly on concentration x, firstly, decreasing from pure FeGe to its minimum (∣∣ks|→0, Hc2→0) at xc≈0.6, and, then increasing again at higher x. Thus, we observe a transformation of the helix structure to the ferromagnet at x→xc at zero field. We concluded that this transformation is caused by different signs of the spin helicity for the compounds with x>xc and x