5. The histochemical muscle fiber types in the normal FDL were studied with standard methods and detailed fiber type counts made. Average innervation ratios for each motor-unit type were estimated from the relative frequencies of the unit types and of the histochemical muscle fiber types associated with them. The estimates for FF+ F (int), FR, and S units were 328, 132, and 180 muscle fibers per motor unit, respectively. These values together with other data permit estimates for the specific tensions for each unit type, which were 3.5, 2.9, and 0.6 kg/cm2 for FF, FR, and S units, respectively. 6. The physiological properties of the three major motor-unit types in FDL are compared with data from studies of five other hindlimb muscles in the cat. The organization of the FDL motor-unit population is most similar to that found in the ankle flexor, tibialis anterior (22), and differs from that in its anatomical synergist, flexor hallucis longus (47). These comparisons are discussed in relation to the patterns of functional usage in the same muscles in intact, behaving animals (38).