The observation of gamma‐ray lines during solar flares is the most convincing evidence that nuclear reactions take place between high energy particles and the solar atmosphere. The application of data from the measurements of these lines is very wide spread. It ranges from information about the acceleration of charged particles to elemental composition determination of the various solar atmospheric layers. After a brief review of the production of the nuclear lines it is shown, how their measurements can be applied in different ares of the solar flare phenomenon.