The object of the study was grasspea (Lathyrus sativus L.) of the Krab variety. The seeds were subjected to the effect of static and alternating magnetic field, treated with a chemomutagene (MNU), and subjected to a combined treatment – magnetic field + MNU. Two different levels of magnetic field intensity (both static and alternating) and three doses of MNU were applied. After the treatments, the seeds were sown into plots in a field experiment to obtain plants of M1 generation. After harvest, the plants were analyzed for yield parameters as compared to control plants. Treatments with magnetic field alone induced, for a majority of the traits studied, a slight stimulation effect or, to a lesser degree, a reduction effect, or else the values of the traits remained on the level of the initial form. In the case of treatment with MNU doses alone, a high level of biological damage was induced, increasing with the use of stronger doses of the mutagene. This was particularly visible for traits directly related to plant fertility. In the combined treatments (magnetic field + MNU), the values of the traits studied, without exception, were lower in comparison with the magnetic field treatments, but for most of the combinations they were higher than for the MNU treatments. This indicates the possibility of using magnetic field treatments in combination with MNU for the reduction of biological damage caused by the motagene, and thus to increase of number of seeds from the M1 generation of plants. Although the differences in the effect of the alternating and static magnetic field were slight, the result obtained suggest a higher effectivness of static field in combined treatments in reducing the level of biological damage induced by the mutagenic agent.