An expression is derived for the height of the stationary boundary layer during stable lapse rate conditions. It satisfies the conventional limits for neutral conditions and for large values of stability. Comparison with acoustic sounder observations near the meteorological mast at Cabauw (the Netherlands) shows that the steady-state height is not attained for large stability values. The observations are also used to investigate how the similarity functions A and B in the resistance laws depend on the stability parameters μ0 = u */f L and Μ = h/L. The function B shows a clear trend as a function of stability, which can be described in terms of μ. The dependence of A is masked by scatter in the data points. The general conclusion leads to the concept of a non-steady boundary layer during stable lapse rate conditions.