This report concerns three unrelated floppy infants, two girls and one boy, each biopsied at the age of 1 month. They were hypotonic since birth and required artificial ventilation. The two girls died at the ages of 4 and 3 1/2 months, respectively, the boy is still alive at the age of 2 years, but requires assisted ventilation. Each of the three infants showed, by muscle biopsy, abundant intranuclear rods, the boy and one girl also had sarcoplasmic rods, which were not present in the other girl's muscle. Absence of sarcoplasmic rods, but the presence of intranuclear rods could also be documented in her autopsied muscle. Using an antibody against alpha-actinin, immunoelectron microscopy showed reaction of the sarcoplasmic and intranuclear rods demonstrating their Z-band origin. To our knowledge, this is the first report on rod myopathy with intranuclear rods only and of an immunoelectron microscopic demonstration of alpha-actinin in intranuclear rods. The presence of intranuclear rods in infants with nemaline myopathy also appears to indicate a grave prognosis of their rod myopathy.