We explore the possibility of achieving one-step unification of the standard model coupling constants within non-supersymmetric and supersymmetric gauge models, which at low energies have only the standard particle content. The constraints are the experimental values of α em , α s and sin 2 θ W at 10 2 GeV, and the lower bounds for FCNC and proton decay rates. The analysis is done in a model-independent way.