In the calculation of stellar models with the Cox–Stewart opacities no convective zones in the outer layers of massive stars appear. The new OPAL opacities (Rogers & Iglesias, 1992) show a significant bump in the opacity near temperatures of log T = 5.2. This opacity effect results in a small convective zone in the envelope of stars with mass ranging from 15 M⊙ to 150 M⊙, apart from possible convective zones caused by ionization. This was also briefly mentioned by Glatzel & Kiriakidis (1993). For stars on the main sequence this zone is small, about 1% of its radius on the zero age main sequence up to 7% at the onset of the core helium burning and contains a negligible amount of mass. For helium burning stars, however, this convective zone moves inward, keeping the same size but containing more and more mass.