Sustainable rates of sebum secretion were measured in twelve subjects with inflammatory acne and in twelve control subjects, matched in age and gender, who had no significant signs of acne. The measurements were made after first depleting the skin of an accumulation of previously secreted sebum by absorption into adherent layers of bentonite clay applied to the center of the forehead for 14 hours. Disks of fine Dacron mesh, embedded in fresh clay, were then applied to the forehead for 3 hours. The disks and adhering clay were then removed and extracted with ether to recover the collected lipids. The sebum recovered during the 3-hour period was measured by quantitative thin layer chromatography. The subjects with acne were found to have an average sustainable sebum secretion rate of 2.51 mg/10 cm2/3 hr, while the control group had an average of 0.81 mg/10 cm2/3 hr. Furthermore, all subjects with acne had secretion rates larger than those of their matched control subjects. The results indicate that a high sebum secretion rate is the decisive factor in inflammatory acne.