Polyclonal antisera were prepared against purified mycelial proteins from Verticillium dahliae, the predominant fungus species in the potato early dying complex. The antisera tested against crude mycelial preparations of Verticillium spp. using indirect enzyme-linked immunosorbent assay (ELISA) reacted positively with 11 of 12 V. dahliae isolates from potato, cotton, and soil, but negatively with one isolate from tomato. The antisera did not react with mycelial proteins from Fusarium spp. from potato and cotton, with a Colletotrichum sp. from potato, or with one isolate of Rhizoctonia solani from sugarbeet. Double antibody sandwich ELISA, using polyclonal antisera, detected V dahliae and V. albo-atrum in infected roots and stems of potato,