[en] The stability of the solar wind against the whistler mode is analyzed. It is shown that the solar wind can become unstable owing to this mode after a distance of 100 R solar mass from the sun. The minimum value of the relative velocity (Usub(r)) between α-particles and protons for the excitation of this instability is the proton thermal velocity α sub(i). The maximum growth rate at 200 R solar mass occurs for the values of the parameters kpsub(i) = 0.3, (Tsub(perpendicular)/Tsub(parallel))sub(i) = 0.3 and Usub(r)/α sub(i) = 0.5. (author)