THERE is agreement in recent papers that testosterone is “glycopexic” and “glycostatic” with respect to several striated muscles (1–3). Early reports on the effects of testosterone on glycogen storage in striated muscles have been reviewed by Leonard (1). Bloom, Lewis, Schumpert, and Shen (4) have shown that cold tricholoroacetic acid (TCA) will consistently extract about 55% of the glycogen normally found in muscle following potassium hydroxide (KOH) digestion. These workers and others (5–9) have shown that tissue levels of TCA soluble and insoluble glycogen vary independently of each other under various physiological conditions. This has led to the concept that muscle glycogen may be comprised of two physiological entities. The present study was undertaken to determine the effects of testosterone propionate (TP) on TCA-soluble and insoluble glycogen, and to determine the relationship between the glycogen changes and the phenomenon of TP induced growth of the levator ani muscle in the rat.