The following organisms were used in the study: Ceratocystis moniliformis (Hedge.) C. Moreau ATCC-12861, obtained from the American type culture collection; C. coerulescens (Mivnch) Bakshi obtained from Dr. K. J. Kessler at the Lake States Forest Experiment Station; C. fimbriata (Ell. & Halst.) Davidson f. platani Walter, obtained from Dr. R. W. Davidson at the Beltsville Forest Disease Laboratory; C. variospora (Davids.) C. Moreau and Thielaviopsis basicola (Berk.) Ferr., from the University of Connecticut culture collection. All of the iso? lates were maintained on potato-dextrose agar slants. The organisms were grown in 250 ml Erlenmyer flasks containing 50 ml of potato-dextrose (5 %) broth and incubated on a rotary shaker at 250 rpm for 4 or 5 days at 25 C. The contents of these flasks then served as inocula for large flasks (2,500 ml) containing 650 ml of potato-dextrose (5%) broth. These flasks were incubated on a reciprocal shaker with a stroke length of 4 inches (88 strokes/min) for 3-4 days at 25 C. The total contents of the large flasks, generally 10 liters, were steam distilled. The carbonyl 2,4-dinitrophenylhydrazone derivatives (2,4DNPH) were made by adding an excess of acidified 2,4-dinitrophenylhydrazine (0.2%, 2,4-DNP in 2N HC1). The distillate containing 2,4-DNP was allowed to stand overnight at room temperature. The