This study examine whether muscle wasting in critically ill patients can be prevented by passive stretching alone in the absence of contractile activity. Five critically ill patients who required a complete neuromuscular blockade for 7 days of ventilator support were studied. One leg of each patient was treated with continuous passive motion (CPM) for three 3-h periods daily while the other leg received only routine nursing care. Fiber atrophy was prevented in the more severely ill patients and there was a slight gain in fiber area (mean increase, +11%) in the CPM limb compared with the control leg, which decreased (mean decrease, -35%) over 7 days. Fiber area was preserved in both fiber types but was more pronounced in type I muscle fibers. Protein loss was significantly less in the CPM limb. There was a significantly greater increase in wet weight per mg DNA in the control limb. However, as an index of wasting, the ratio of protein to DNA decreased similarly in both limbs. Passive stretching can preserve the architecture of muscle fibers. Whether it can prevent muscle wasting remains uncertain.