SUMMARYThe barley biotype ofSeptoria nodorumwas recovered from isolates of the wheat biotype after 2–6 passages through barley. Shifts in the population of the two biotypes during host passage were determined by isolating single spores after passage and observing changes in symptom expression on both hosts. The number of passages required before the barley biotype was recovered varied with the fungus isolate and barley cultivar. Attempts to recover the wheat biotype from isolates of the barley biotype during several passages through wheat were unsuccessful when 105to 106conidia m1‐1were used as inoculum. However, the wheat biotype was recovered from two isolates of the barley biotype during a single passage when a very high concentration of conidia (>1012ml‐1) were used as inoculum. From the results of this study and a previous report by the author, the biotype ofS. nodorumon barley which occurs in the southeastern United States appears to be largely restricted to b