Seven series of laboratory and glasshouse experiments were conducted to investigate different methods of testing and studying the effect of several chemicals, root exudates of germinating crop seeds, and their interactions on Orobanche cernua. Compared to experiments in an incubator, better results were obtained when seed germination was tested in the presence of seedlings of host plants under glasshouse conditions. GR24 at 0.1 and 1.0 mg kg-1 was the most effective in stimulating the germination of O. cernua seeds, followed by gibberellic acid at 10 and 20 mg kg-1. Without the addition of chemicals, trap crops strongly increased germination, with green gram (Vigna radiata) and sunn hemp (Crotalaria juncea) being particularly effective. There was an interaction between the effects of chemicals and trap crops. A positive effect of trap crops was observed even when there was already strong stimulation by GR24 at 1.0 mg kg-1, but under these conditions, trap crops were less effective at 0.1 mg kg-1 GR24. No differences between cultivars in their effect on O. cernua germination could be detected within one host plant species.