Marigolds (Tagetes erecta and T. patula) or sea ambrosia (Ambrosia maritima) as intercropped plants with soybean (Glycine max) cv. Giza 21 infected with Meloidogyne incognita, the root-knot nematode, significantly (P £ 0.05 and 0.01) reduced nematode numbers on soybean as indicated by the percentage reduction of galls, developmental stages and egg masses in roots and juveniles (J2) in soil. Marigolds significantly (P £ 0.05 or 0.01), in most cases, increased plant growth parameters of soybean, but sea ambrosia had an adverse effect on plant growth parameters. Addition of chopped green leaves of sea ambrosia to the soil planted to soybean significantly (P £ 0.05 and/or 0.01) reduced M. incognita reproduction and development. Sea ambrosia also had an adverse effect on soybean plant growth.