Methods for the evaluation of root rot disease in sugarbeet caused by pathogenic fungi historically have relied on visu­ al assessment. In an initial attempt to develop complemen­ tary means to detect and quantitate root rot disease caused by Aphanomyces cochlioides, antiserum was produced in rabbits that had been immunized with a cell-wall prepara­ tion of this organism. Specificity tests using enzyme-linked immunosorbant assay (ELISA) indicate that the antiserum is strongly reactive with both A. cochlioides and A. euteich­ es, but weakly with oomycetes non-pathogenic to sugar­ beet, with fIlamentous fungi that infect sugarbeet, or with extracts prepared from healthy sugarbeet. A 1:2,000 dilu­ tion of the serum was sufficient to readily detect A. cochlioides in infected sugarbeet seedlings. Sugarbeet roots obtained from a piling station in Minnesota, USA that exhibited adult root rot symptoms characteristic of those caused by A. cochlioides tested negative for the presence of this pathogen. The antiserum provides an additional tool for the detection of A. cochlioides in field and greenhouse­ grown sugarbeet and for immunochemical investigations of root rot disease. Additional Key Words: Beta vulgaris, Black-root, ELISA, detection, oomycete