A detailed study of both individual cotton plants and data from the overall performance of large fumigation plots, resulted in convincing evidence that early season infection by Verticillium wilt may drastically reduce yield. Yield reductions were reflected in reduced production per plant and in bolls of lighter weight. Where infection of individual plants occurred from seedling to harvest, and occurred more severely on some plants than on others, yield reductions resulted from the production of fewer bolls per foot of row, and lighter boll weight averages. Fumigation obviously controlled soil-borne pathogens other than Verticillium—some perhaps unknown—so the total effect of fumigation evidenced in the second year may not have resulted from Verticillium wilt control alone. High plant vigor and dense plant populations undoubtedly reduced yields in fumigated plots.