The present studies were aimed at determining the allopathic interspecies interactions of weed grains from wild oats (Avena fatua L.) and red fescue (Festuca rubra L.) on winter wheat and winter rye germination and seedling growth. Preliminary studies on inter-crop influences were done in a laboratory using developing dishes. Those tests allowed us to determine the allelopathic effect of the tested grain weed species on the germinating ability of seeds of other grain crop species as well as on the length of root, coleoptiles length, fresh and air dry matter of roots and coleoptiles. The results showed that the neighborhood of wild oats (Avena fatua L.) and red fescue (Festuca rubra L.) decrease germinating ability of winter wheat by about 4% as compared to the pure stand. There was no inhibiting influence of the neighboring red fescue on wheat germinating ability. There was observed a negative influence of the tested weed species on winter rye germinating ability but a significant difference was only observed between control dishes and treatment with red fescue. The research showed that the neighbourhood of wild oats inhibited the length of coleoptile and root seeds of winter wheat and their fresh and air dry matter stronger than red fescue. Winter rye was more sensitive to the neighbourhood of red fescue than wild oats.