EMG and MB are complementary investigations. They agreed completely in four cases but in the rest of the cases there was uncertainty as to the primary process based on the results of electrophysiological studies. In only one case was there a clear discordance between electrophysiological studies and muscle biopsy. We suggest that muscle biopsy should be performed more frequently as it establishes the diagnosis and thus the prognosis with more certainty than EMG in some patients. EMG is much more difficult in the ICU and more susceptible to confounding technical factors, but remains indispensable for the diagnosis of neuromuscular transmission defects.