The effect ionizing radiation and hypomagnetic conditions have on the lettuce seeds of Lactuca sativa L is studied on the 120-cm cyclotron at Moscow State University's Skobeltsyn Institute of Nuclear Physics. The seeds are irradiated with deuterons having an energy of ~13.7 MeV at doses of 65 Gy, 0.55, and 5.5 kGy. They are then germinated under conditions of a geomagnetic field weakened by 50 and 10 3 times. The change in the response of seeds to radiation exposure depending on the attenuation of the geomagnetic field is analyzed.