The results indicate that the trend found previously of an increase in boundary-layer transition Reynolds number with increase in model cooling continued to higher Reynolds numbers. The highest transition Reynolds number obtained with cooling was 28,500,000. At this Reynolds number, the classical Tollmien-Schlichting wave type of boundary-layer number, the instability was apparently overshadowed by surface roughness effects. The results indicated that, when transition was fixed by surface irregularities or airstream flow disturbances, cooling was not effective in obtaining laminar flow behind the irregularity or disturbances.