The survey which was carried out in alfalfa plantations at Ismailia Agricultural Research Station in seasam 1998/99, indicated that the inci­dence of Verticillium wilt ranged from 1.9 to 16.6%. The highest per­centage was recorded in June, while the lowest was in February. No wilt symptoms was found in January. Aphids were found throughout the year and their population ranged in between 1.3 and 13.2 insect per plant. Highest population was found in March, whereas the lowest was in Au­gust and September. Natural percentage of field aphids contaminated with Verticillium ranged from 1.3 to 7.5 % and caused 16.7 and 33.3 % infection, while artificially ones (laboratory strain) resulted in 76.7 and 90% wilted plants for cut and uncut planted, respectively. Spraying cut and uncut plants with the spores of the fungus caused 43.3 and 6.6% wilted plants, respectively. Treatment with Verticillium spores reduced the length and weight of shoot and root as well as protein contents in cut and to a greater extent in the uncut plants. Both aphids (laboratory strain) free from Verticillium and the artificially contaminated caused greater reductions of the growth rates.