Substances that are moderately to strongly comedogenic in the rabbit ear model test have been found to be capable of inducing comedones in the human model described in this report. The test substances are applied under occlusion for one month to the upper part of the backs of young adult, black men who have large follicles. The degree of follicular hyperkeratosis is assessed by a noninvasive "follicular biopsy" techniques, employing a fast-setting cyanoacrylate glue to remove the follicular contents. The rabbit model is more sensitive than the human. Substances that are weakly comedogenic in the rabbit are probably safe for human use with the possible exception of acne-prone persons.