In view of minimising the use of pesticides in agriculture, scientific researchers all over the world are oriented to other “alternative”,“nonchemical” weed control measures which are required to be efficient as chemicals but should be beneficial to the environment. Although allelopathy interactions between plants were observed in the 3rd century BC, allelopathy and allelochemicals started to play an important role in agriculture in the 20th. The aim of this paper was to investigate the allelopathic effect of two important nonnative weed species in Croatia, Abutilon theophrasti Med.(ABUTH) and Datura stramonium L.(DATST). Both of the weeds are very competitive in corn crops and cause great losses in corn yields. Laboratory experiments were conducted in 2004. and 2005. In the first experiment allelopathic effect of aqueous extract of fresh shoot and leaves, and separately aqueous extract of roots of Abutilon theophrast Med. on germination and early growth of corn (Zea mays L.) were examined. In the second experiment allelopathic effect of above part of plant of both weeds were examined only. Aqueous extracts of Abutilon theophrasti Med. inhibited strong germination, radicle and coleoptile length of corn. On the other side promoting effect on radicle length was noticed by aqueous extract of Datura stramonium L. Germination of corn, measured 3, 6 and 10 days after treatments, was inhibited by aqueous extracts of above ground part of plants of both weed species.