Pea seeds of three varieties were conditioned to a moisture content between 11.5 and 19.5%. With a specially adapted universal instrument for strength testing (INSTRON) single seeds were compressed under quasi-static load while recording force and deformation until an a priori desired value of energy was applied. The physical shape of the stressed seeds was evaluated by visual examination and by interpretation of the recorded data during the compression test. The physiological shape was evaluated by a germination test. With increasing moisture content the seeds reacted as viscid bodies. Moist seeds were capable of more deformation and absorbed more energy until the tissue was ruptured. Dry seeds had a higher deformation resistance. The measured force, deformation and energy at the rupture point was significantly different between the tested varieties. The relationship between the applied energy and germination followed an optimum curve as germination decreased in the succession of 15.5, 17.5, 19.5, 13.5 and 11.5% moisture content. Seeds with cracks in the embryo could have an intact testa and did not necessarily fail in germination. Only with dry seeds could all cracks be detected with the help of the force-deformation-curve of the compression test.