The present paper deals with the problem of allelopathic interactions among medicinal plants. The investigations were carried out on following medicinal species: Capsella bursa- -pastoris and Stellaria media as the donors also Origanum majorana and Ocimum basilicum as the acceptors of allelopathic compounds. The effect of water extracts from the investigated weeds on the germination and on the cotyledones stadium and two-leaf stage was tested. The biotest revealed that the 2.5% exstract concentration of Capsella bursa-pastoris and Stellaria media influences the negative effect on two-leaf stage of Origanum majorana and Ocimum basilicum.