Scale-scheme ambiguities in the Brodsky-Lepage-Mackenzie procedure

The recently proposed method of Brodsky, Lepage and Mackenzie for ''eliminating scale ambiguities in perturbative QCD'' yields different results in different renormalization schemes. We show that one cannot make a scheme-independent separation of fermion loop effects from other types of higher-order correction. The case of #betta# decay is discussed particularly. (orig.)